OAuth JSON error for Google Analytics Importer

I’ve followed the directions to set up an OAuth instance in Google Cloud and successfully downloaded my json token. The redirect URI is internal, tunneled because I’m attempting to set up a Mautic instance on a VPS solely for the purpose of backing up Google Analytics data to a private server.

When I hit save, I get " Missing or invalid client configuration, please reupload. " as the error.

The redirect URI I have in the OAuth is:

I’ve also tried on the non-tunneled port, port 80. Both yield the same error.

The OAuth credentials are enabled for the Google Analytics UA Analytics API per the Mautic instructions. What am I doing wrong?