If you are on the S21 then the beta is now over and you should be able to install the final full release on your phone.
If you already have then please do the following.
Delete the Cache and Data from under the App Properties.
Uninstall GPay.
Reboot.
Reinstall GPay.
This should hopefully fix your issue.
If you are still running a beta version then check to see why you have not received the final non beta version and go from there.
GPay and a few security intensive apps have never worked on Samsung betas as apps like this look for officially signed f/w which Samsung betas are not. Samsung is apparently looking to fix this on the future but seeming as its always been like this I would not hold your breath.
Hope the above helps!
Have a great weekend! 👍🏼
