Thanks for using Microsoft Q&A !!
Can you please check if
- Your application has been configured as a Multitenant app in you application registration page
- If the setting "User assignment required" is enabled in the Azure AD Enterprise application and the user is not the list of allowed users.
- You are sending your requests to common endpoint
https://login.microsoftonline.com/common
Please let me know if you still see any issues.
Thanks
Saurabh