Bootstrap modal does not show up after submit

Hello I’m trying to display a bootstrap modal after they select a withdrawal amount and click on submit button which also updates the withdraw row in the database, I tried echo the full bootstrap html but it still blinks and doesn’t stay as it is supposed to be

So far it only blinks and doesn’t stay at all.

<head>
  <title>Bootstrap Example</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>
</head>


<?php
// Include config file
require_once "config.php";
 
// Define variables and initialize with empty values
$withraw = "";
$withraw_err = "";
 
// Processing form data when form is submitted
if($_SERVER["REQUEST_METHOD"] == "POST"){
 
      // Validate Withrawal
    if(empty(trim($_POST["withraw"]))){
        $withraw_err = "Please Choose a Amount.";     
    } else{   
            $withraw = trim($_POST["withraw"]);
            }

    // Check input errors before inserting in database
    if(empty($withraw_err)){
        
        // Prepare an insert statement
        $sql = "UPDATE users SET withraw = (?) WHERE id = 211";

        if($stmt = mysqli_prepare($link, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "s", $param_withraw);
            
            // Set parameters
           
            $param_withraw  = $withraw;
           
            
            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
               echo "<script>
         $(window).load(function(){
             $('#myModal').modal('show');
         });
    </script>";
            } else{
                echo "Something went wrong. Please try again later.";
            }

            // Close statement
            mysqli_stmt_close($stmt);
        }
    }
    
    // Close connection
    mysqli_close($link);
}
?>

       <label><h1 class="h1">withraw</h1></label>
        

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


              <div class="form-group <?php echo (!empty($withraw_err)) ? 'has-error' : ''; ?>">
               

                <div class='selectt'><select name="withraw" class="form-control" value="<?php echo $withraw; ?>"><option >Choose Amount</option>
        <option value="500">500</option>
        <option value="1000">1,000</option>
        <option value="1500">1,500</option>
        <option value="2000">2,000</option>
        <option value="2500">2,500</option>
                <option value="3000">3,000</option>
        <option value="3500">3,500</option>

</select>
        
        </div>
                <span class="help-block"><?php echo $withraw_err; ?></span>
            </div>    
        
        

    

          <div class="form-group">
                <button type="submit" class="btn btn-info btn-lg" data-toggle="modal" data-target="#myModal" value="Submit">
                    Withraw <i class='fa fa-check-circle'></i> </button>
                <button type="reset" class="btn btn-default" value="Reset"><i class='fas fa-redo'></i> Reset </button>
            </div>

        </form>
   
   

 <div id="myModal" class="modal fade" role="dialog">
  <div class="modal-dialog">

    <!-- Modal content-->
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal">&times;</button>
        <h4 class="modal-title"><img src="loading.svg" class="loaderr"> Pending Approval</h4>
      </div>
      <div class="modal-body">
        <p>Hello User, your request to withdraw has been sent to the Company.
        
        <br>
       <br>
       You will be notified when the withdrawal status has been updated.
      <br>
      <br>
      <font color="red">Note:</font> Do not resubmit a withdrawal request until the next 48hours
        </p>
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
      </div>
    </div>

  </div>
</div>

</div>
    
 

Thank you so much, I’m sorry the code is bulky