Hello Mark,
I'm really sorry to see that your question hasn't been answered. I've been trying to solve the exact same error for days, surfing the Google Help Center, but I still have the same problem in both Moodles (one is a 3.3.4 and the other a 3.4) I manage. I also manage the Gsuite accounts and have done the integration with the code and the secret pass myself. I've tryied Google Chrome and Microsoft Edge, and nothing seems to be working.
If you have figured it out, PLEASE let me know how.
Thanks,
Marina Pindar