As you are on the Beta software, there are various things that will have issue or not work.
One of those things is Google Pay. As its not finalised software, it won't have the security certification yet.
To withdraw from the Beta program is a bit of a process. So hopefully you backed up your device before entering the Beta Program
Below is a copy of the withdrawal procedure that's in the Beta Members section
11. How do I remove the beta software?
1. To withdraw from the Beta programme, you must apply for withdrawal through Samsung Members application on your device.
("Settings > One UI Beta Programme status > Withdraw" menu)
2. To remove the beta software, perform a rollback to the previous release version, using the Smart Switch PC Version on your computer. The rollback resets the device and removes data generated during beta testing.
Note: If you backed up your device data to your computer with Smart Switch, you can restore the data after the rollback process. To perform the rollback, connect the device to your computer with a USB cable. On the computer, launch the Smart Switch application, and select "Downgrade".
If you need assistance in having your software rolled back to the latest approved version you can call Samsung Service Center.
– Call Center UK : 0333-000-0333 / Ireland : 0818-717-100