Bootstrap 4.3.1 dropdown login form redirect upon success - authentication

Question

I am building a site where users can login via a Bootstrap Dropdown, i did have it working, it would log user in and refresh the whole page with login session BUT if user entered wrong creds it wouldn't stay open and alert them. I got around this by putting the login form in an iframe in the dropdown but it's no longer starting the session - any ideas please? I'm trying to not be vague so here is the code in the iframe and the actual URL below that - thank you :)
<div class="header_login_form_dropdown">Login</div>
<form name="login" action="" method="post" class="form">
<div class="form-group">
<label class="login_form_dropdown" for="lopc_username">Email</label>
<input type="email" class="form-control" id="lopc_username" placeholder="email#company.com" name="lopc_username">
</div>
<div class="form-group">
<label class="login_form_dropdown" for="lopc_password">Password</label>
<input type="password" class="form-control" id="lopc_password" name="lopc_password">
</div>
Forgot password
<button type="submit" name="submit" class="btn btn-primary login_btn">LOGIN</button>
<div style="padding:15px 0 15px 0; border-top: 2px solid #eee; font-size: 14px; color: #696969">
New customer? Register here
</div>
<?php
if (isset($_POST['submit']))
{
include('../265451/92631043.php');
$lopc_username = mysqli_real_escape_string($conn,$_POST['lopc_username']);
$lopc_password = mysqli_real_escape_string($conn,(md5($_POST['lopc_password'])));
$lopc_last_login = date("Y-m-d H:i:s");
$query = "SELECT * FROM lopc_reg_users WHERE lopc_username = '$lopc_username' AND lopc_password = '$lopc_password' ";
$result = mysqli_query($conn,$query);
if(mysqli_num_rows($result) == 1)
{
$_SESSION['lopc_username'] = $_POST['lopc_username'];
$lopc_username = $_SESSION['lopc_username'];
$query2 = "UPDATE lopc_reg_users SET lopc_last_login = '$lopc_last_login' WHERE lopc_username = '$lopc_username' ";
$result2 = mysqli_query($conn,$query2);
//header("Location: ".$_SERVER['PHP_SELF']);
?>
<script>
window.parent.location.reload();
</script>
<?php
exit;
}
else
{
echo '<div class="login_error">Username or password does not exist.</div>';
}
}
?>
</form>
https://littleorangeprinting.co.uk/2021
Login: test#test.com
Pass: testing4321