Выдает ошибку Fatal error: Uncaught Error

Выдает ошибку

Fatal error: Uncaught Error: Call to undefined function mysql_connect() in 
C:\OSPanel\domains\dblog\admin\includes\connection.php:4 Stack trace: #0 
C:\OSPanel\domains\dblog\admin\includes\header.php(4): require_once() #1 
C:\OSPanel\domains\dblog\admin\register.php(1): include('C:\\OSPanel\\doma...') #2 {main} thrown in 
C:\OSPanel\domains\dblog\admin\includes\connection.php on line 4

Вод код с той строки

$con = mysql_connect(DB_SERVER,DB_USER, DB_PASS) or die(mysql_error());

В чем ошибка?