having this added into the GPGS documentations, at the very least some kind of a note to let devs know that this is a possible fix.
That’s an excellent idea. Should be part of the standard implementation checklist for GPGS and surely it will be soon.
As a side note, this issue results from the error handling on Google’s part. Returning “Internal error” doesn’t say anything about what’s wrong. It should definitely be more specific. It’s like the Corona simulator just said “there’s an error somewhere in your code” without giving any specifics.