Payment processor integration is quite a complex multi-stage procedure. However, the result is worth the efforts. All the works related to integration with a payment processor have to be done in constant close cooperation with the processor’s representatives. The processor has to open the project, assign a responsible specialist, provide you with test credentials, test cards, test scenarios, approve the results of all tests, and confirm the successful integration with a certification letter.
As an integrator you have to follow all the processor’s requirements, carefully monitor all the development works and testing processes at all stages, and provide all the necessary documentation in time.
Additional information on this issue is provided in the respective article at Paylosophy Blog.