PHP - Query From Post Method Works For Text Box But Not Selection List

* Display related posts.
*
* @return void
*/
function stag_related_posts() {
    global $post;
    if( stag_rcp_user_has_no_access() )
        return;
    if( ! stag_theme_mod( 'post_settings', 'show_related_posts' ) )
        return;
    $tags = wp_get_post_tags( $post->ID );
    if ( count( $tags ) ) {
        $tags_ids = array();
        foreach($tags as $individual_tag) {
            $tag_ids[] = $individual_tag->term_id;
        }
        $query = new WP_Query( array(
            'tag__in' => $tags_ids,
            'post__not_in' => array( $post->ID ),
            'posts_per_page' => absint( stag_theme_mod( 'post_settings', 'related_posts_count' ) ),
            'caller_get_posts' => 1
        ) );
        // Add filter to attach 'post-grid' class
        add_filter( 'stag_showing_related_posts', '__return_true' );
        if( $query->have_posts() ) :
            echo '<section class="related-posts" data-layout="2-2-2-2">';
            while( $query->have_posts() ) : $query->the_post();
                get_template_part( 'content', get_post_format() );
            endwhile;
            echo '</section>';
        endif;
    }
    wp_reset_query();
    remove_all_filters( 'stag_showing_related_posts' );
}

I have this code here. i wanted to know how i can be able to make multiple selections from the returned data from the database and how to save them

 <select name="troom"  multiple class="form-control" required>
                                    <option  selected="true" disabled="disabled">--Select a room--</option>
                                    


                                        
                                        $records =mysqli_query($con, "select * from room where TRoom not in (select TRoom from roombook where cin <= '$checkout' and cout >= '$checkin');");
                                        
                                        while ($data = mysqli_fetch_array($records)) {
                                            echo "<option value='" . $data['TRoom'] . "'>" . $data['TRoom'] . "</option>"; //displaying data in option menu
                                        }
                                    }

                                    ?>

                                </select>

I've used a showQuery() method for years which accepted a SQL string and data array.  Sometimes, I just have the PDO statement and I need to add temporary script just to keep track of the SQL string.  Was looking at debugDumpParams() today which prompted me to create the new showStmtQuery() method.  My approach of extracting the table from debugDumpParams's printed results is a little clunky.  Any recommendations?  Could/should other information from debugDumpParams's output be used?  I typically don't use bound parameters but know I should more often.  Suggestions how this could be changed to work with bound parameters?  Thanks

function showQuery(string $sql, arrray $data, bool $keepLineBreaks=false):string {
    $keys = [];
    $values = [];
    foreach ($data as $key=>$value) {
        $keys[] = is_string($key)?'/:'.$key.'/':'/[?]/';
        $values[] = is_numeric($value)?$value:"'$value'";
    }
    $sql = preg_replace($keys, $values, $sql, 1, $count);
    return $keepLineBreaks?$sql:str_replace(array("\r", "\n"), ' ', $sql);
}
function showStmtQuery(\PDOStatement $stmt, array $data, bool $keepLineBreaks=false):string {
    ob_start();
    $stmt->debugDumpParams();
    $sql = ob_get_contents();
    ob_end_clean();
    //$sql = strtok(substr($sql, strpos($sql, '] ')+2), "\n");
    $start=strpos($sql, '] ')+2;
    $sql = substr($sql, $start, strpos($sql, "\nParams:") - $start);
    return showQuery($sql);
}

$data=[5,50];
$sth = $pdo->prepare('SELECT *
    FROM my_table
WHERE id > ? AND id < ?');
echo(showStmtQuery($sth, $data).PHP_EOL);   //SELECT * FROM my_table WHERE id > 5 AND id < 50

$data=['lowId' => 5, 'highId' => 50];
$sth = $pdo->prepare('SELECT *
    FROM my_table
WHERE id > :lowId AND id < :highId');
echo(showStmtQuery($sth, $data).PHP_EOL);   //SELECT * FROM my_table WHERE id > 5 AND id < 50

I use AJAX method to get the value for `$month` from the year-month selection in my page.  The year-month is pass correct correctly when it gets into my PHP code. But i am not sure how do i get the value and use it for my sql condition. 

I'm trying to plot a graph using Chart JS according to the year-month selection from the user. when the user select "2021-03" all the order that is made in the month of March will be plotted into the graph. There's no data shown in my page now and i do not know how can i query it. Can anyone enlighten me how can i do it? Because i do not know what mistake did i made here. Any kind of explanation will be appreciated. Thanks!

This is the code that i use for year-month selection 

<div class="col-2 my-auto">
                <input type="month" id="month" class="form-control" value="<?php echo date('Y-m'); ?>">
              </div>

               <div class="col-2 my-auto">
                <button type="button" class="btn btn-info" onclick="loadchart();">
                  <i class="nc-icon nc-zoom-split"></i>
                </button>
              </div>

This is the AJAX method

 <script type="text/javascript">
function loadchart()
{
 $('#spin1').show();
 var month= $('#month').val();
  var data = {    
    month: month,
  }
  $.ajax({
    method:"GET",
    data:data,
    url:"includes/loadchart.php",
    success:function(data)
    {
        $('#loadchart').html(data);
    }
  });

}

this is my loadchart.php

<?php
include '../session.php';
if(isset($_GET['month']))
{
    $months = $_GET['month'];
?>
<?php
  $days = array();
  $gross_sales = array();
  $average_sales = array();
  $type = CAL_GREGORIAN;
  $month = date('n'); 
  $year = date('Y'); 
  $day_count = cal_days_in_month($type, $month, $year); 
  for ($i = 1; $i <= $day_count; $i++) {
      $sql = "SELECT *, SUM(purchase_price) as purchase_price FROM ordered_items WHERE DAY(order_datetime) = '$i' AND MONTH(order_datetime) = MONTH('".$months."') AND YEAR(order_datetime) = YEAR('".$months."') AND order_status = 5 ";
    $query = $conn->query($sql);
    $total = $query->num_rows;
    $row = $query->fetch_assoc();
    if($row['purchase_price'] != 0)
    {      
      $gross_sales[] = $row['purchase_price'];
    }
      
    else if ($row['purchase_price'] == 0 && $i <= date('d')) {
      $gross_sales[] = 0;
    }

    $average_sales[] =  $row['purchase_price'] / $day_count;

    $day =  $i.'/'.$month; 
    array_push($days, $day);
  }

  $days = json_encode($days);
  $daily_gross_sales = json_encode($gross_sales);
  $average_gross_sales =  json_encode($average_sales);
?>
  <script>
    const colors = {
      colorcode: {
        fill: '#51cbce',
        stroke: '#51cbce',
      },
    };
    var ctx2 = document.getElementById("attChart").getContext("2d");
    const attChart = new Chart(ctx2, {
      type: 'line',
      data: {
        labels: <?php echo $days; ?>,
        datasets: [{
          label: "Gross Sales: RM",
          fill: true,
          pointBackgroundColor: colors.colorcode.stroke,
          borderColor: colors.colorcode.stroke,
          pointHighlightStroke: colors.colorcode.stroke,
          borderCapStyle: 'dot',
          pointRadius: 5,
          pointHoverRadius: 5,
          pointStyle: 'dot',
          data: <?php echo $daily_gross_sales; ?>,
          showLine: true
        },
        {
          label: "Average Sales: RM",
          fill: true,
          pointBackgroundColor:   '#FF0000',
          borderColor: ' #FF0000 ',
          pointHighlightStroke: '#FF0000',
          borderCapStyle: 'dot',
          pointRadius: 5,
          pointHoverRadius: 5,
          pointStyle: 'dot',
          data: <?php echo $average_gross_sales; ?>,
          showLine: true
    }
        ]
      }
    <?php   
}
?>

I do not know why my query from the loadchart.php is incorrect. Please help me with this advice me on this issue thanks!

  $sql = "SELECT *, SUM(purchase_price) as purchase_price FROM ordered_items WHERE DAY(order_datetime) = '$i' AND MONTH(order_datetime) = MONTH('".$months."') AND YEAR(order_datetime) = YEAR('".$months."') AND order_status = 5 ";