Using the Payment Gateway through the Payrexx API is the most customisable integration option.
Before you start developing you need a few things...
First you have to choose one of the available payment types. This will be needed once you start building your Gateway
If you want to make one-time payments, you can skip this step. Because one-time is the default type.
Finally! You can now start developing.
Detailed process description from the Gateway creation until after payment completion:
All about the Payrexx Webhook:
Shape and content of your transaction or subscription Webhook: