http 500 and Stack trace:#0 {main}

now the only problem is http 500 and

Stack trace:

#0 {main}

thrown in /home/topwax/public_html/index.php on line 25

[11-May-2021 07:11:46 UTC] PHP Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /home/topwax/public_html/index.php:25

Stack trace:

#0 {main}

thrown in /home/topwax/public_html/index.php on line 25

this is the line 25: mysql_connect( $db_host, $db_username, $db_password) or die(mysql_error());

Is this a follow-up? If so please, reply to your original thread to avoid confusion.