Play Store keeps rejecting our app with a PlayStoreError SERVICE UNAVAILABLE error

We're trying to submit our app for the first time. It's never been submitted before. Several times now, the Play Store has rejected our app because the in-app subscription purchase flow returns a "PlayStoreError Failed to fetch products. It is a proxy of the Google BillingClient error: SERVICE UNAVAILABLE" error.

It's working fine from our test license accounts... is this something people have run into before? Could the Play Store tester be in an unsupported country? Or maybe their phone doesn't have Play Store on it? Or maybe they are not in our license testers group so they are getting an error because our app hasn't been submitted yet?

We appealed it the first time and they gave us an exception without any explanation... is this like a known issue when publishing a new app?