Hi there Carmen!
Don here from Shopify. :)
We make integration with third-party gateways available for our platform, though it is actually the gateway providers themselves that would be responsible for supporting and maintaining that integration.
Just reach out to PayGate directly to let them know what is happening on your site and ask what you might be able to do together to get this working for your store. :)
We're also available 24/7 via our support site to field any other questions you might have.
All the best!