PHP - Mysqli Insert From Form

Hi, I have an app that access a MySQL database via a php script.
I noticed that INSERT was returning error but the data was being recorded successfully.
I finally traced the problem to be related with the line 
echo $conn->affected_rows;   

For some reason when it is an SQL INSERT it returns -11 but as I said the INSERTS executes successfully.

The app requesting the service sends in sequence:

char* txtSQL[]={"INSERT INTO activity (mac,jd,date,time,area,type,value) VALUES ('a9c4952de6b4',2458454,'2018-12-01','10:22','Area0002','h',130)",
                            "INSERT INTO activity (mac,jd,date,time,area,type,value) VALUES ('a9c4952de6b4',2458454,'2018-12-01','10:22','Area0002','h',130)",
                            "INSERT INTO activity (mac,jd,date,time,area,type,value) VALUES ('a9c4952de6b4',2458454,'2018-12-01','10:22','Area0002','h',130)",
                            "INSERT INTO activity (mac,jd,date,time,area,type,value) VALUES ('a9c4952de6b4',2458454,'2018-12-01','10:22','Area0002','h',130)",
                            "UPDATE activity set value=333 where value=130",
                            "SELECT sum(value) from activity where mac='a9c4952de6b4'",
                            "DELETE from activity WHERE value=333"};

I set a monitor to check what was being returned and got:

query=INSERT INTO activity (mac,jd,date,time,area,type,value) VALUES ('a9c4952de6b4',2458454,'2018-12-01','10:22','Area0002','h',130)
HttpResponse:  -   httpResponseCode: -11
query=INSERT INTO activity (mac,jd,date,time,area,type,value) VALUES ('a9c4952de6b4',2458454,'2018-12-01','10:22','Area0002','h',130)
HttpResponse:  -   httpResponseCode: -11
query=INSERT INTO activity (mac,jd,date,time,area,type,value) VALUES ('a9c4952de6b4',2458454,'2018-12-01','10:22','Area0002','h',130)
HttpResponse:  -   httpResponseCode: -11
query=INSERT INTO activity (mac,jd,date,time,area,type,value) VALUES ('a9c4952de6b4',2458454,'2018-12-01','10:22','Area0002','h',130)
HttpResponse:  -   httpResponseCode: -11
query=UPDATE activity set value=333 where value=130
HttpResponse: 4 *   httpResponseCode: 201   -------------------------------------->As can be seem the INSERTS above returned error but worked OK
query=SELECT sum(value) from activity where mac='a9c4952de6b4'
HttpResponse: 1379 *   httpResponseCode: 200
query=DELETE from activity WHERE value=333
HttpResponse: 4 *   httpResponseCode: 201

The  PHP script do ing the job i s as be low :

<?php
include('connection.php');

//these are just in case setting headers forcing it to always expire 
header('Cache-Control: no-cache, must-revalidate');

error_log(print_r($_POST,TRUE));

if( isset($_POST['query']) && isset($_POST['key']) ){                                   //checks if the tag post is there and if its been a proper form post
  header('Content-type: application/x-www-form-urlencoded');
  if($_POST['key']==$SQLKEY){                                                           //validates the SQL key
    $query=urldecode($_POST['query']);
    if(get_magic_quotes_gpc()){     //check if the worthless pile of crap magic quotes is enabled and if it is, strip the slashes from the query
      $query=stripslashes($query);
    }
    $conn = new mysqli($DB_ADDRESS,$DB_USER,$DB_PASS,$DB_NAME);    //connect

    if($conn->connect_error){                                                           //checks connection
      header("HTTP/1.0 400 Bad Request");
      echo "ERROR Database Connection Failed: " . $conn->connect_error, E_USER_ERROR;   //reports a DB connection failure
    } else {

      $result=$conn->query($query);                                                     //runs the posted query                        

      if($result === false){
        header("HTTP/1.0 400 Bad Request");                                             //sends back a bad request error
        echo "Wrong SQL: " . $query . " Error: " . $conn->error, E_USER_ERROR;          //errors if the query is bad and spits the error back to the client
      } else {
        if (strlen(stristr($query,"SELECT"))>0) {                                       //tests if it's a SELECT statement
          $csv = '';                                                                                // bug fix Undefined variable: csv
          while ($fieldinfo = $result->fetch_field()) {
            $csv .= $fieldinfo->name.",";
          }
          $csv = rtrim($csv, ",")."\n";
//********************************          echo $csv;                                                                    //prints header row
          $csv = '';

          $result->data_seek(0);
          while($row = $result->fetch_assoc()){
            foreach ($row as $key => $value) {
              $csv .= $value.",";
            }
            $csv = rtrim($csv, ",");                                                 //."\n";
          }
          echo $csv;                                                                    //prints all data rows
        } else {
          header("HTTP/1.0 201 Rows");
          echo $conn->affected_rows;       //if the query is anything but a SELECT, it will return the number of affected rows (INSERT IS  RETURNING -11)
        }
      }
      $conn->close();                                          //closes the DB
    }
  } else {
     header("HTTP/1.0 400 Bad Request");
     echo "-Bad Request";                                       //reports if the secret key was bad
  }
} else {
        header("HTTP/1.0 400 Bad Request");
        echo "*Bad Request";
}
?>

Any help will be much appreciated.
Thanks

Paulo Borges

/** insert data array */
public function insert(array $arr)
{

if ($arr)
{
$q = $this->make_insert_query($arr);
$return = $this->modifying_query($q);
$this->autoreset();
return $return;
}
else
{
$this->autoreset();
return false;
}
}

/** insert query constructor */
protected function make_insert_query($data)
{
$this->get_table_info();
$this->set_field_types();
if (!is_array(reset($data)))
{
$data = array($data);
}
$keys = array();
$values = array();
$keys_set = false;
foreach ($data as $data_key => $data_item)
{
$values[$data_key] = array();
$fdata = $this->parse_field_names($data);
foreach ($fdata as $key => $val)
{
if (!$keys_set)
{
if (isset($this->field_type[$key]))
{
$keys[] = '`' . $val['table'] . '`.`' . $val['field'] . '`';
}
else
{
$keys[] = '`' . $val['field'] . '`';
}
}
$values[$data_key][] = $this->escape($val['value'], $this->is_noquotes($key), $this->field_type($key), $this->is_null($key),
$this->is_bit($key));
}
$keys_set = true;
$values[$data_key] = '(' . implode(',', $values[$data_key]) . ')';
}
$ignore = $this->ignore ? ' IGNORE' : '';
$delayed = $this->delayed ? ' DELAYED' : '';
$query = 'INSERT' . $ignore . $delayed . ' INTO `' . $this->table . '` (' . implode(',', $keys) . ') VALUES ' . implode(',',
$values);
return $query;
}

$db = Sdba::table('users');
$data = array('name'=>'adam');
$db->insert($data);