It is Google themselves choosing to prevent GrapheneOS from passing the validation checks required to make GPay work (which is the app that makes the actual pay

It is Google themselves choosing to prevent GrapheneOS from passing the validation checks required to make GPay work (which is the app that makes the actual payment). Wallet is there, you can hold digital cards, and transit cards, and your Ikea member card, etc. It's GPay that won't work to do the payment. And it's Google the one being a bully and deliberately making you think like that towards any alternative that's not in their list of approved systems that can be used in your own phone.