How do I call an external php non WordPress class into functions.php?

Include this in your theme functions,

 <?php
    $includes_path="the root folder you want to call";
    require_once $includes_path . 'the_class_you_are_calling.php';
  ?>

Also make sure you have the privileges access… I know it’s dummy but I’ve been there done that…

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