I have created an app that reads and updates my personal RingCentral address book. It has been running since August. This week after a flurry of errors one day last week, I started getting the error...

Error: Access not granted or expired.

at Service_.getAccessToken(Service:454:11)

I have fixed the problem that was generating the production error (badly formed address in the source data). I am still getting the OAUTH error. I have tried suspending and reactivating the app. No change. I have checked the OAUT credentials. They have not changed.