API for taking payments

My client lost his merchant processor and just switched over to a new one who does not support ZenCart directly, they provided API details for their merchant account but I can't find any documentation or explanation how to connect the API information they provided to ZenCart, any help would be greatly appreciated as we're stuck and do not want to rebuild on another platform.

It would be less work to get your client to use an already supported processor like Authorize or Square or PayPal.

Even with detailed API documentation, writing a payment module is a huge job that requires detailed knowledge and takes a lot of time. I don't recommend it!