Hello @Caroline , thank you for reaching out. It looks like the REDIRECTURI/REPLYURL mentioned in the request that is being submitted to AAD, doesn't contain a valid ReplyURL or RedirectURI string, and hence it's erroring out. It can also be that whatever is being sent in the request, doesn't matchup with the entry stored in AAD, hence AAD is throwing this error.
Based on the details shared above, I did pull up the backend logs and I do see a mismatch in the replyURL. Please find the details below:
AppID: d9cd28f8-ecfd-4225-b4ce-0cb9184b9344
Redirect URI passed in the request: https://10.15.0.28/auth/microsoft_office365/callback
Redirect_uri configured in the App Registration: https://forum.xx.krxxxx.xx/auth/microsoft_office365/callback/
Note: Since RedirectURI is sensitive information for your registered app, hence I have tried hiding the data and keeping only what can help you recognize your actual redirect Uri.
Hope this helps.
Do let us know if this helps and if there are any more queries around this, please do let us know so that we can help you further. Also, please do not forget to accept the response as an Answer; if the above response helped in answering your query.