PHP - Validation Error In Php

I am a new developer, trying to figure out what causing a memory error. The code goes through registered appointments and depends on the service ID, I have to free a 45 minutes for another service to be booked. Now, once I book an appointment for any of the services that can have 45 minutes free spot, the website takes forever to load the hours but doesn't show them, instead I get this error

A PHP Error was encountered Severity: Error Message: Maximum execution time of 120 seconds exceeded

foreach ($appointments as $appointment) { foreach ($periods as $index => &$period) { $appointment_start = new DateTime($appointment['start_datetime']); $appointment_end = new DateTime($appointment['end_datetime']); if ($appointment_start >= $appointment_end) { continue; } $period_start = new DateTime($date . ' ' . $period['start']); $period_end = new DateTime($date . ' ' . $period['end']); $serviceId=$appointment['id_services']; $color1=1; $color2=2; $color3=3; $color4=4; $color5=5; $color6=6; $color7=7; $color8=8; $color9=9; $color10=10; $color11=11; $color12=12; $color13=13; $color14=14; $color15=15; $color16=16; $color17=17; $color18=18; $color19=19; $period_s=''; $period_e=''; if ($appointment_start <= $period_start && $appointment_end <= $period_end && $appointment_end <= $period_start) { // The appointment does not belong in this time period, so we will not change anything. continue; } else { if ($appointment_start <= $period_start && $appointment_end <= $period_end && $appointment_end >= $period_start) { // The appointment starts before the period and finishes somewhere inside. We will need to break // this period and leave the available part. //open slot for services 45,45,45 if($serviceId == $color1 || $serviceId == $color3 || $serviceId == $color7 || $serviceId == $color9|| $serviceId == $color10 || $serviceId == $color11 || $serviceId == $color12){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['start'] = $appointment_end->format('H:i'); } //Open slot for service 45,45,60 else if($serviceId == $color2 || $serviceId == $color8){ $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['start'] = $appointment_end->format('H:i'); } // // //Open slot for service 30,45,45 else if($serviceId == $color4 || $serviceId == $color6 ||$serviceId == $color16 || $serviceId == $color18){ $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['start'] = $appointment_end->format('H:i'); } // // //Open slot for service 30,45,60 else if($serviceId == $color5 || $serviceId == $color17){ $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['start'] = $appointment_end->format('H:i'); } // // //Open slot for service 60,45,45 else if($serviceId == $color13 || $serviceId == $color15){ $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['start'] = $appointment_end->format('H:i'); } // // //Open slot for service 60,45,60 else if($serviceId == $color14 ){ $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['start'] = $appointment_end->format('H:i'); } // //for the rest of services else { $period['start'] = $appointment_end->format('H:i');} } else { if ($appointment_start >= $period_start && $appointment_end < $period_end) { // The appointment is inside the time period, so we will split the period into two new // others. unset($periods[$index]); if($serviceId == $color1 || $serviceId == $color3 || $serviceId == $color7 || $serviceId == $color9|| $serviceId == $color10 || $serviceId == $color11 || $serviceId == $color12){ $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_start->format('H:i'), 'end' => $appointment_start->format('H:i') ]; $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $periods[] = [ 'start' => $appointment_end->format('H:i'), 'end' => $period_end->format('H:i') ]; } // //Open slot for service 45,45,60 else if($serviceId == $color2 || $serviceId == $color8){ $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_start->format('H:i'), 'end' => $appointment_start->format('H:i') ]; $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $periods[] = [ 'start' => $appointment_end->format('H:i'), 'end' => $period_end->format('H:i') ]; } // // //Open slot for service 30,45,45 else if($serviceId == $color4 || $serviceId == $color6 ||$serviceId == $color16 || $serviceId == $color18){ $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_start->format('H:i'), 'end' => $appointment_start->format('H:i') ]; $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $periods[] = [ 'start' => $appointment_end->format('H:i'), 'end' => $period_end->format('H:i') ]; } // // //Open slot for service 30,45,60 else if($serviceId == $color5 || $serviceId == $color17){ $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_start->format('H:i'), 'end' => $appointment_start->format('H:i') ]; $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $periods[] = [ 'start' => $appointment_end->format('H:i'), 'end' => $period_end->format('H:i') ]; } // // //Open slot for service 60,45,45 else if($serviceId == $color13 || $serviceId == $color15){ $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_start->format('H:i'), 'end' => $appointment_start->format('H:i') ]; $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $periods[] = [ 'start' => $appointment_end->format('H:i'), 'end' => $period_end->format('H:i') ]; } // // //Open slot for service 60,45,60 else if($serviceId == $color14 ){ $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_start->format('H:i'), 'end' => $appointment_start->format('H:i') ]; $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $periods[] = [ 'start' => $appointment_end->format('H:i'), 'end' => $period_end->format('H:i') ]; } //for other services once The code is completely correct else{ $periods[] = [ 'start' => $period_start->format('H:i'), 'end' => $appointment_start->format('H:i') ]; $periods[] = [ 'start' => $appointment_end->format('H:i'), 'end' => $period_end->format('H:i') ]; } } else if ($appointment_start == $period_start && $appointment_end == $period_end) { if($serviceId == $color1 || $serviceId == $color3 || $serviceId == $color7 || $serviceId == $color9|| $serviceId == $color10 || $serviceId == $color11 || $serviceId == $color12){ unset($periods[$index]); $period_s= $appointment_start; $period_s->modify('+45 minutes'); $period_e= $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } //Open slot for service 45,45,60 else if($serviceId == $color2 || $serviceId == $color8){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } // // //Open slot for service 30,45,45 else if($serviceId == $color4 || $serviceId == $color6 ||$serviceId == $color16 || $serviceId == $color18){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } // // //Open slot for service 30,45,60 else if($serviceId == $color5 || $serviceId == $color17){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } // // //Open slot for service 60,45,45 else if($serviceId == $color13 || $serviceId == $color15){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } // // //Open slot for service 60,45,60 else if($serviceId == $color14 ){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ];} // //for the rest of services else { unset($periods[$index]);} // The whole period is blocked so remove it from the available periods array. } else { if ($appointment_start >= $period_start && $appointment_end >= $period_start && $appointment_start <= $period_end) { // The appointment starts in the period and finishes out of it. We will need to remove //the time that is taken from the appointment. if($serviceId == $color1 || $serviceId == $color3 || $serviceId == $color7 || $serviceId == $color9|| $serviceId == $color10 || $serviceId == $color11 || $serviceId == $color12){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $period['end'] = $appointment_start->format('H:i'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } //Open slot for service 45,45,60 else if($serviceId == $color2 || $serviceId == $color8){ $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $period['end'] = $appointment_start->format('H:i'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } // // //Open slot for service 30,45,45 else if($serviceId == $color4 || $serviceId == $color6 ||$serviceId == $color16 || $serviceId == $color18){ $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['end'] = $appointment_start->format('H:i'); } // // //Open slot for service 30,45,60 else if($serviceId == $color5 || $serviceId == $color17){ $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['end'] = $appointment_start->format('H:i'); } // // //Open slot for service 60,45,45 else if($serviceId == $color13 || $serviceId == $color15){ $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['end'] = $appointment_start->format('H:i'); } // // //Open slot for service 60,45,60 else if($serviceId == $color14 ){ $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; $period['end'] = $appointment_start->format('H:i'); } // for the rest of services else{ $period['end'] = $appointment_start->format('H:i'); } } else { if ($appointment_start >= $period_start && $appointment_end >= $period_end && $appointment_start >= $period_end) { // The appointment does not belong in the period so do not change anything. continue; } else { if ($appointment_start <= $period_start && $appointment_end >= $period_end && $appointment_start <= $period_end) { //Open slot for service 45,45,45 if($serviceId == $color1 || $serviceId == $color3 || $serviceId == $color7 || $serviceId == $color9|| $serviceId == $color10 || $serviceId == $color11 || $serviceId == $color12){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } //Open slot for service 45,45,60 else if($serviceId == $color2 || $serviceId == $color8){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+45 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ]; } // //Open slot for service 30,45,45 else if($serviceId == $color4 || $serviceId == $color6 ||$serviceId == $color16 || $serviceId == $color18){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ];} //Open slot for service 30,45,60 else if($serviceId == $color5 || $serviceId == $color17){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+30 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ];} // // //Open slot for service 60,45,45 else if($serviceId == $color13 || $serviceId == $color15){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-45 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ];} // // //Open slot for service 60,45,60 else if($serviceId == $color14 ){ unset($periods[$index]); $period_s= clone $appointment_start; $period_s->modify('+60 minutes'); $period_e= clone $appointment_end; $period_e->modify('-60 minutes'); $periods[] = [ 'start' => $period_s->format('H:i'), 'end' =>$period_e->format('H:i') ];} else{ unset($periods[$index]); } } } } } } } } } return array_values($periods); }

$sql = "SELECT shoplist.*, store_master.store_name, item_master.item_name
           FROM shoplist, store_master, item_master
           WHERE     shoplist.store_id = store_master.store_id
                   AND shoplist.item_id = item_master.item_id";

$sql = "SELECT shoplist.*, store_master.store_name, item_master.item_name 
		FROM shoplist, store_master, item_master 
		ORDER BY purchased_flag ASC, 
				purchase_later_flag ASC, 
				shopper1_buy_flag ASC, 
				shopper2_buy_flag ASC, 
				store_name ASC) 
		WHERE 	shoplist.store_id = store_master.store_id 
				AND shoplist.item_id = item_master.item_id";

                    <?php
                        /*
                        $sql = "SELECT shoplist.*, store_master.store_name, item_master.item_name
                                FROM shoplist, store_master, item_master
                                WHERE     shoplist.store_id = store_master.store_id
                                        AND shoplist.item_id = item_master.item_id";
                        */
                    
                        $sql = "SELECT shoplist.*, store_master.store_name, item_master.item_name
                                FROM shoplist, store_master, item_master
                                ORDER BY FIND_IN_SET(purchased_flag ASC,
                                                 purchase_later_flag ASC,
                                                 shopper1_buy_flag ASC,
                                                 shopper2_buy_flag ASC,
                                                 store_name ASC)
                                WHERE     shoplist.store_id = store_master.store_id
                                        AND shoplist.item_id = item_master.item_id";
                        $result = $pdo->query($sql);                        
                        
                        // foreach ($pdo->query($sql) as $row) {
                        foreach ($result as $row) {
                            echo '<tr>';
                                print '<td><span class="filler-checkbox"><input type="checkbox" name="IDnumber[]" value="' . $row["idnumber"] . '" /></span></td>';

Hello ,

I have a made a PHP website where users signup and send their Date of Birth and gets an OTP on their email after signup.

The OTP is recieved but when we enter the OTP this problem occurs 

Error! Something went wrong 

and I am facing this error in the error log

PHP Fatal error: Uncaught Error: Object of class DateTime could not be converted to string 

This is my config.php code

<?php
    session_start();
?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Confirmation Page - Kanha Stories</title>

    <style>
        body
        {
            background-color: #330000;
            background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='100%25' height='100%25' viewBox='0 0 800 400'%3E%3Cdefs%3E%3CradialGradient id='a' cx='396' cy='281' r='514' gradientUnits='userSpaceOnUse'%3E%3Cstop offset='0' stop-color='%23D18'/%3E%3Cstop offset='1' stop-color='%23330000'/%3E%3C/radialGradient%3E%3ClinearGradient id='b' gradientUnits='userSpaceOnUse' x1='400' y1='148' x2='400' y2='333'%3E%3Cstop offset='0' stop-color='%23FA3' stop-opacity='0'/%3E%3Cstop offset='1' stop-color='%23FA3' stop-opacity='0.5'/%3E%3C/linearGradient%3E%3C/defs%3E%3Crect fill='url(%23a)' width='800' height='400'/%3E%3Cg fill-opacity='0.4'%3E%3Ccircle fill='url(%23b)' cx='267.5' cy='61' r='300'/%3E%3Ccircle fill='url(%23b)' cx='532.5' cy='61' r='300'/%3E%3Ccircle fill='url(%23b)' cx='400' cy='30' r='300'/%3E%3C/g%3E%3C/svg%3E");
            background-attachment: fixed;
            background-size: cover;
            padding: 20px;
            width: 100vw;
            height: 100vh;
            display: flex;
            align-items: center;
            justify-content: center;
            color:#ffffff;
            overflow-x: hidden;
        }
        .cont
        {
            padding: 20px 40px;
            position: relative;
            border-right: 4px solid rgb(184, 182, 182);
            border-bottom: 4px solid rgb(184, 182, 182);
            border-radius: 15px;
            display: flex;
            flex-direction: column;
            align-items: center;
        }
        #left{
            float: left;
        }
        #right{
            float: right;
        }
        input{
            margin: 10px 0px;
        }
        s{
            padding: 5px;
        }
        .error{
            padding: 5px;
            color: #ffffff;
        }
        .resend{
            color: rgb(14, 14, 196);
            padding: 5px;
        }
        .s:hover{
            cursor: pointer;
            background-color:gray;
            color: rgb(243, 237, 237);
            border-radius: 5px;
        }
    </style>

</head>
<body>

    <?php
        $code="";
        $err="";
        $error="";
        if(($_SERVER["REQUEST_METHOD"]=="GET" && $_SESSION['xyz'] === 'xyz') || isset($_POST['verify']) || isset($_POST['resend']))
        {
            unset($_SESSION["xyz"]);
            if($_SERVER["REQUEST_METHOD"] ==="POST")
            {
                if(isset($_POST['verify']))
                {
                    if(empty($_POST['code']))
                    {
                        $err="Enter the code!";
                    }
                    else
                    {
                        $code=$_POST['code'];
                        if(password_verify($code,$_SESSION['code']))
                        {
                            $name=$_SESSION['name'];
                            $email=$_SESSION['email'];
                            $tel=$_SESSION['tel'];
                            $dob=$_SESSION['dob'];
                            $password=$_SESSION['password'];
                            $age_category=$_SESSION['age_category'];
                            
                            require_once('./all_utils/connection.php');
                            $sql="INSERT INTO identity_table(name,email,password,tel,dob,age_category) VALUES ('$name','$email','".$password."','$tel','$dob','$age_category')";
                            if(mysqli_query($conn,$sql) === TRUE) 
                            {
                                unset($_SESSION["name"]);
                                unset($_SESSION["password"]);
                                unset($_SESSION["dob"]);
                                unset($_SESSION["tel"]);
                                unset($_SESSION["age_category"]);
                                
                                header("location:welcome/welcome.php");
                            }
                            else
                            {
                                $err="Error! Something went wrong";
                            }
                        }
                        else
                        {
                            $err="Incorrect code!";
                        }

                    }
                }
                elseif(isset($_POST['resend']))
                {
                    require_once('./all_utils/mail.php');
                    $error="OTP has been sent again!";
                }
            }
        }
        else{
            header("location:signup.php");
        }
    ?>

    <div class="cont">
        <h2> Email Verification</h2>
        <form action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']) ?>" method="POST">
            <label for="verification">Enter the 5 digit code</label>
            <br/>
            <p> Didn't got the mail?  Please check your spam folder </p>
            <input type="text" name="code" placeholder="Eg. 12345" value="<?php echo $code; ?>">
            <br/>
            <div class="error"><?php echo $err; ?></div>
            <div class="resend"><?php echo $error;?></div>
            <input type="submit" name="resend" class="s" id="left" value="Resend OTP">
            <input type="submit" name="verify" class="s" id="right" value="Verify">
        </form>
    </div>
</body>
</html>

This is my signup.php code

<?php
    session_start();
    if(!empty($_SESSION['email']))
    {
        require_once('./all_utils/connection.php');
        $query="SELECT * FROM identity_table WHERE email='".$_SESSION['email']."'";
        $result=mysqli_query($conn,$query);
        if(mysqli_fetch_assoc($result))
        {
            header("location:welcome/welcome.php");
        }
    }

?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>SignUp - Kanha Stories</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        body {
            width: 100vw;
            height: 100vh;
            display: flex;
            align-items: center;
            background-color: #ff9d00;
            background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='100%25' height='100%25' viewBox='0 0 1600 800'%3E%3Cg stroke='%23000' stroke-width='66.7' stroke-opacity='0' %3E%3Ccircle fill='%23ff9d00' cx='0' cy='0' r='1800'/%3E%3Ccircle fill='%23f27d00' cx='0' cy='0' r='1700'/%3E%3Ccircle fill='%23e55f00' cx='0' cy='0' r='1600'/%3E%3Ccircle fill='%23d84400' cx='0' cy='0' r='1500'/%3E%3Ccircle fill='%23cb2c00' cx='0' cy='0' r='1400'/%3E%3Ccircle fill='%23bf1600' cx='0' cy='0' r='1300'/%3E%3Ccircle fill='%23b20300' cx='0' cy='0' r='1200'/%3E%3Ccircle fill='%23a5000e' cx='0' cy='0' r='1100'/%3E%3Ccircle fill='%2398001c' cx='0' cy='0' r='1000'/%3E%3Ccircle fill='%238b0027' cx='0' cy='0' r='900'/%3E%3Ccircle fill='%237e0030' cx='0' cy='0' r='800'/%3E%3Ccircle fill='%23710037' cx='0' cy='0' r='700'/%3E%3Ccircle fill='%2364003b' cx='0' cy='0' r='600'/%3E%3Ccircle fill='%2358003c' cx='0' cy='0' r='500'/%3E%3Ccircle fill='%234b003a' cx='0' cy='0' r='400'/%3E%3Ccircle fill='%233e0037' cx='0' cy='0' r='300'/%3E%3Ccircle fill='%23310030' cx='0' cy='0' r='200'/%3E%3Ccircle fill='%23210024' cx='0' cy='0' r='100'/%3E%3C/g%3E%3C/svg%3E");
            background-attachment: fixed;
            background-size: cover;
            overflow-x: hidden;
        }

        .cont {
            color: #ffffff;
            width: 500px;
            margin: auto;
        }

        h2 {
            color: #ffffff;
            text-align: center;
            padding: 1.5px;
        }

        .error {
            text-align: center;
            padding: 20px;
            font-size: 1rem;
            color: rgb(233, 76, 76);
        }

        form {
            font-size: 1.2rem;
            /* width: 40%; */
            /* margin: auto; */
        }
        .in{
            margin: 5px 0;
        }

        input {
            border: 2px solid white;
            padding: 10px;
            margin: 5px 0;
            font-size: 1rem;
            width: 100%;
        }

        input:hover {
            border: 2px solid rgb(228, 81, 81);
            cursor: text;
        }

        p,a{
            text-align: center;
            font-size: 1rem;
        }
        a{
            color: deepskyblue;
            font-size:20px;
        }

        #s{
            text-decoration:none;
            border-radius: 12px;
        }
        #s:hover {
            cursor: pointer;
        }

        a {
            text-decoration: none;
        }
        
        @media only screen and (max-width: 600px){
            .cont{
                width: 300px;
            }
            .error,input{
                font-size: 0.8rem;
            }

        }
        @media only screen and (max-width: 400px){
            .cont{
                width: 70%;
            }
            h2{
                font-size: 1.3rem;
            }
            a,p{
                font-size: 0.7rem;
            }
            label{
                font-size: 1.0rem;
            }
            input{
                padding: 4px;
            }

        }
    </style>
</head>
<body>

    <?php

        $name="";        
        $email="";
        $tel="";
        $dob="";
        $err="";
        
        $name_err="";
        $email_err="";
        $tel_err="";
        $dob_err="";
        $password_err="";
    if($_SERVER["REQUEST_METHOD"]=="POST")
       {
            if(isset($_POST['signup']))
            {
                if(empty($_POST['name']) || empty($_POST['dob']) || empty($_POST['tel']) || empty($_POST['email']) || empty($_POST['password']))
                {
                    if(empty($_POST['name']))
                    {
                        $name_err="Name is required!";
                    }
                    else{
                        $name=$_POST['name'];
                    }
                    if(empty($_POST['email']))
                    {
                        $email_err="Email is required!";
                    }
                    else{
                        $email=$_POST['email'];
                    }
                    if(empty($_POST['tel']))
                    {
                        $tel_err="Contact Number is required!";
                    }
                    else{
                        $tel=$_POST['tel'];
                    }
                    if(empty($_POST['dob']))
                    {
                        $dob_err="D.O.B is required!";
                    }
                    else{
                        $dob=$_POST['dob'];
                    }
                    if(empty($_POST['password']))
                    {
                        $password_err="Password is required!";
                    }
                }
                else
                {
                    $today = new DateTime(date('m.d.y'));
                    $dob = new DateTime($_POST['dob']);
                    $diff1 = $today->diff($dob);
                    $age = $diff1->y;
                    if($age > 15 || $age <3)
                    {
                        $dob = $_POST['dob'];
                        $dob_err = "Age criteria not satisfied , child's age must be between 3-15 years";
                    }
                    else
                    {
                        require_once("./all_utils/connection.php");
                        $email=$_POST['email'];
                        $query="SELECT * FROM identity_table WHERE email='".$email."'";
                        $result=mysqli_query($conn,$query);

                        if(mysqli_fetch_assoc($result))
                        {
                            $err="Email alredy registered!";
                            $name=$_POST['name'];
                            $email=$_POST['email'];
                        }
                        else
                        {
                            if($age < 7)
                            {
                                $_SESSION['age_category'] = '1';
                            }
                            else
                            {
                                $_SESSION['age_category'] = '2';
                            }
                            $_SESSION['name']=$_POST['name'];
                            $_SESSION['email']=$_POST['email'];
                            $_SESSION['password'] = password_hash($_POST['password'],PASSWORD_DEFAULT);
                            $_SESSION['tel']=$_POST['tel'];
                            $_SESSION['dob']=$_POST['dob'];
                            $_SESSION['xyz']='xyz';
                            require_once("all_utils/mail.php");
                            header("location:conf.php");
                        }
                    }
                }
            
            }
        }

    ?>

    <div class="cont">
        <h2>SignUp - Kanha Stories</h2>

            <form action="<?php echo htmlspecialchars($_SERVER['PHP_SELF'])?>" method="POST">

            <span class="error"><?php echo $err; ?></span>
            <br/>

            <label for="name">Name</label><br />
            <input type="text" name="name" placeholder="Enter your name" value="<?php echo $name; ?>">

            <span class="error"><?php echo $name_err; ?></span>
            <br/>

            <label for="email">Email</label><br />
            <input type="email" name="email" placeholder="Enter your Email ID" value="<?php echo $email; ?>">


            <span class="error"><?php echo $email_err;?></span>
            <br/>

            <label for="tel">Mobile Number</label><br />
            <input type="tel" name="tel" placeholder="Enter Mobile Number" value="<?php echo $tel; ?>">


            <span class="error"><?php echo $tel_err;?></span>
            <br/>

            <label for="date">D.O.B. of Child &nbsp; (Click on Calander icon)</label><br />
            
            <input  type="date" name="dob" placeholder="Enter date of birth " value="<?php echo $dob;?>">

            <span class="error"><?php echo $dob_err;?></span>
            <br/>

            <label for="password">Password</label><br />
            <input type="password" name="password" placeholder="Enter your Password">


            <span class="error"><?php echo $password_err; ?></span>
            <br/>
            

            <div class="sub">
            <input type="submit" name="signup" id="s"  placeholder="Submit"><br />
            </div>
        </form>
        <p>Already registered? <a href="./login.php">log in here</a></p>
    </div>
</body>
</html>

I don't know what I can do now , Please try to give me the solutions as soon as possible. Thanks