[Fix] Modern authentication failed here, but youll still be able to sign in. Your status code is 4c7 - Microsoft Teams

Modern authentication failed here, but you'll still be able to sign in. 

Your status code is 4c7

If you receive the above message with code 4c7 in Teams application when trying to login via your companies AD FS (active directory) the most common reason could be that when AD FS was deployed the Forms Authentication was not enabled. This option is not enabled by default.

In order to fix this issue, the Forms Authentication option needs to be enabled using the AD FS MMC (Microsoft Management Console) snap-in on the computer that has the local copy of AD,

1. Under Navigation Pane look for Authentication Policies,
2. Under Details Pane -> Actions -> Select Edit Global Primary Authentication,
3. Under Intranet tab select Forms Authentication.
4. Click on OK to apply changes.