I ran the REST API Authentication demo located at 

https://community.appeon.com/index.php/codeexchange/powerserver/296-rest-api-authentication

and selected

demo.appeon.com/psrestauthentication/

I selected Azure AD button followed by Authorization Code button
This opened up the Microsoft Sign In with default Username and Password screen.

I then had to change the password to continue as it had expired – PLEASE NOTE - I added a capital X to beginning of password so it is now XPowerserver2021~!@#
After entering the new password and clicking on sign in. The following message appeared.

Request Id: bf203094-09c3-4f8f-ab8d-a94945935f00
Correlation Id: ed671d44-fa71-43b3-a09c-5757a0033c01
Timestamp: 2023-09-25T19:20:44Z
Message: AADSTS700016: Application with identifier 'b9b65d02-efd8-4410-9bb0-f8ef6eff7180' was not found in the directory 'Default Directory'. This can happen if the application has not been installed by the administrator of the tenant or consented to by any user in the tenant. You may have sent your authentication request to the wrong tenant.

Additional Screenshots below

Thanks

Jim