Hi, I faced with the same issue. I prepared a merchant ID, verified my domain, create a merchand identity cert and so on. I get the error: Could not create SSL/TLS secure channel. I have another merchant identity cert and domain and if I try it everything works. The same code and the different cert/merchant info pair. Why???

Matt's answer sounds good. But it doesn't help. I went throw required steps, prepared merchant Id, merchant identity cert and so on but it doesn't work. I have an application where Apple Pay works fine. I use it's code to prepare the second application, but it doesn' work with new merchant Id data. I get "Could not create SSL/TLS secure channel."