ERROR
“error”: “invalid_grant”,
“error_description”: “AADSTS501051: Application ‘5669c008-20c0-4118-AAAAAAA(APP-01) is not assigned to a role for the application ‘5669c008-20c0-4118-8f45-AAAAAAAA'(APP-01).
“error_codes”: [501051]
SOLUTION 1
Go to Portal > Active Directory > Enterprise Applications > > Choose your App > Set User assignment required to No
SOLUTION 2
Go to Users > Add User