Hi, we are using Unity's own IAP with the Amazon store active:
So far we have not encountered any problems with it, but we wanted to verify that there are no known issues that you are aware of that might affect the experience of our users.
I have found some threads related to the same topic but those are 2+ years old and without much details, some more up to date information would be great to have before we make a decision.
We will evaluate adding Amazon's IAP SDK soon but at the moment we are limited on time and if Unity's IAP is enough we would prefer to release with it.
Thank you for your help