I had to change things on my google cloud account side.
- Select application type Web application
- add https://www.google.com to the “Authorized redirect URIs”.
redirect_uri_mismatch simply says that the redirect_uri you transmit with the request isn’t identical with the uri you saved as an Authorized redirect URI
Please double check you changed to the new ID in the openhab config. form.
As to the version, I really have no knowledge what relevant changes were made in which version. From the github thread I linked I took the impression that things were modified for the current milestone. You may want to read there and compare with your situation.
I was an a milestone version already when I started to get errors.
Good luck!