I have a console application that connects to a SharePoint site to retrieve some data. It uses a Client ID and Client Secret generated on the AppRegNew page for that site. The app has been granted full rights to the Site Collection. These are relatively new ID's so they have not expired.
Recently it began failing with a "Token request failed", "Remote server returned an error: (401) Unauthorized."
We are using a commonly used TokenHelper class to retrieve the token.
We did have some older App Client ID's hanging around so I deleted the old one's using the AppPrincipals page, however I can still perform a lookup on them in the AppInv page so I don't believe they are actually removed.
Is there something I can check on the SharePoint side to try and determine why this Client ID cannot request a Token successfully?
