Good example - and goes to show how miserable it is when these folks kill stuff off.

Sounds like a good reason to integrate with Authorize.net or another vendor that provides platform agnostic APIs that let you pick your own payment vendor (at much lower cost than Amazon's payment offerings).

It was never our primary payment method, but we had higher conversion rates with it. We had Authorize.net at the time, then added PayPal PayFlow and Stripe. I actually authored a payment abstraction library that would try providers in order of priority and fall back gracefully, avoiding double charges and even abstracting over payment status, refunds, etc.

> I actually authored a payment abstraction library that would try providers in order of priority

Were you storing PANs then?

No, the retry logic was in-tandem between the client and a separate server endpoint.