Your Google Pay mileage may vary, I keep trying to add my cards from 2 different banks and both failed. Factory resetted twice, completely stock (not rooted/unlocked), but Google Pay says that I need to call my bank each time I add my cards, but when I call both banks, they say that there's no issues on my account.
I can still re-add my cards back to my old phone, so definitely a Redmi K20 Pro bug.
EDIT: Contacted Google support, they say my phone is not passing verification, even though its brand new and out of the box, they escalated the case and I'm waiting for them to reply.