Login Error from Microsoft about Incorrect Username

While logging into EUM Portal, or a SharePoint site, as a user registered with EUM, Microsoft might display an error saying the username may be incorrect.

For Signing in with Email

As the error message states, this might be a misspelled email address that Microsoft does not recognize. Please check the email used to sign in, correct it if need be, and continue to sign in.

For Signing in with Mobile Number (SMS Authentication)

One might see an incorrect username message from Microsoft when trying to sign in with a registered mobile number that normally receives an SMS with a One-Time Passcode to sign in.

This could be because Microsoft blocks any user from logging in whose email address has the root domain verified in Microsoft Entra (Azure AD).

In the example below, demo.com is a verified domain in Microsoft Entra (Azure AD) and any Guest User using a Subdomain of this would see the "username may be incorrect" error message from Microsoft while signing in.