Hello,
We can fix payment gateway bugs.
Our skills: Php, Yii, Laravel, HTML, CSS, Bootstrap, MySQL, CMS Wordpress, Opencart, Prestashop, Drupal, Joomla, etc. You can see our profile here https://www.freelancer.com/u/Webln .
Please, send us a link to the payment gateway and your website where you have bugs.
With regards,
WebIn team.