If you're encountering an "Invalid Account" error, follow these steps to troubleshoot.
1. Go to Azure AD admin center, select Enterprise applications.
2. Select the application that you added for Foxit Admin console and open it.
3. Select Single sign-on, and then choose SAML to check Attributes & Claims.
Note that the Editor uses the email account to log in, so please confirm that the user principal name item is the email account.
4. If email is set to user.mail, confirm that the email item is the user's email account. But I recommend setting the email to user.userprincipalname. Typically, user principal name is the email account.
If the above information hasn't been helpful, please try the following solution.
The main cause for the persisting error is if the Namespace URI is not blank.
This conflicts with the UPN calling to the Admin Console for proper username login. Removing the Namespace in the attribute claim should allow the users to activate it properly. Thanks.
Hope this article can help you. If you still have questions or comments about SSO login, please contact Foxit support (via creating a support ticket) for further assistance. Thank you.