Hello, like everything that works online, payment processing can sometimes experience technical problems. That is why it is so important that the payment gateway provides quality technical support that can help you at any time. Usually, support is provided through several communication channels: chat, phone, email. By the way, I can recommend you to visit
PayAdmit: Online Payment Processing | Payment system for the site, the service for accepting payment to read information about one of the most popular and reliable payment gateways.