GrapheneOS is often better for testing apps due to it being trivial to test with and without google services, most of the hardening options can be used for debugging and provide a crash log to determine what failed, and there is an easily accessible log viewer available in app info.
There are alternatives for payments (scroll the thread, maybe look up on GOS discussion site).
If you live in the EU then you can use curve pay which can tap to pay.
Why is no tap to pay significant enough to stop you from switching to a phone that is private and secure? You can just carry a card and tap—they're tiny.