Issue in Creating Dynamic URL in custom wordpress plugin

Since the page does not exist in WordPress Pages that’s why 404, you can achieve your goal by using URL Parameter Like: https://example.com/pincode/?pin_code=110045.

And in PHP use:

if( isset( $_GET['pin_code' ) ) {
 //Continue your logic.
}

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)