Drupal 7 fix your buttons ajax cart not adding products

drupal 7 to fix the button for ajax adding of product to cart.
Description of the error:
https://drupal-coder.ru/blog/drupal-7-uskorenie-vremeni-generacii-stranic-internet-magazina-na-32

Beats error Page is not available on the Website bus-avto.com.ua still can not process that request.
HTTP ERROR 500

Hello.

In the logs this error:
[Wed Jul 15 13:56:59 2020] [error] [client 193.28.177.122] PHP Parse error: syntax error, unexpected ? in /home/u7503/domains/bus-avto.com.ua/sites/all/modules/custom/custom.module on line 55, referer: http://bus-avto.com.ua/admin/modules?filter=cus&enabled=1&disabled=1&req...

The error occurs because the code in line 55. There is a?? operator, which was added in php 7.0 https://www.php.net/manual/ru/migration70.new-features.php.
As an option or you need the code to be rewritten for php 5, or change the php version to 7.2.

The website
http://bus-avto.com.ua/