This is exactly my story. But NFC payments don't work on Graphene.
AFAIK the only reason why Google Pay NFC payments don't work is because Google Pay keeps a list of hardware and OS that's allowed to use that feature, and GrapheneOS is not in that list. It's not an OS limitation.
There was an open issue to spoof this data so that Google Pay NFC payments, among other Google features behind this check, would work. But it looks like it got discarded 2 days ago: https://github.com/GrapheneOS/os-issue-tracker/issues/1986
They recommend that app developers adopt the much stronger and vendor-neutral Android hardware attestation API instead.