Adding new type of external payment gateway

Hello,

I want to ask - we are coding studio (developing and maintaining few Shopify apps). We have new client, who is Slovakian payment gateway provider.

He wants to add / make a way to use his payment gateway for his clients on Shopify.

I cannot find proper information if it is still possible and where to find info / API informations / requirements.

  • I find something, this for now, there is no way to implement other then actual implemented payment gateways

  • I find something in API, that it is possible but with liquid (but what I know is, that this is soon deprecated, right?) - they are using classic redirect method, that payment is made on their site.

So, is there anyone, who could explicitly answer me, if it is possible, if yes = some information for API / requirements?

Thank you all!!