Hi,
I had an issue with my integration which turned out to be a change in methodology that wasn’t properly documented, and my error sounds similar. My code worked perfectly in the sandbox, but wouldn’t work in the live environment, and it turns out you HAVE to set the OAUTH Redirct URI in the App setting in the developer dashboard.
The only place I found this referred to was here: Forthcoming API OAuth Restriction change
If it is this, please complain to them as they said they would update the docs, and as far as I can tell, they haven’t yet. I wasted at least a day on this.