JIm, I shared your comments with my software team and this is their reply...
"Good morning Dr. N Patrick. We've been digging into this issue but still could not find where the source of the error is. We're now suspecting that something changed on Invision end and caused the link to break, because we have not changed anything on our end, especially not without your explicit direction.Could you follow up with Invision and ask them if they recently updated their OAuth protocol in a significant way, and how? My development team shared the following screenshot for you to attach in your follow up message to them.