Hi @Gavin Renn , can you please follow this thread and let me know your results?
"The reply URL needs to be registered in the Azure Portal to create the connection to the application. Go to Azure Active Directory > App Registrations > My App > Authentication > and configure the URL that the user should be directed to after sign in. The reply URL in the portal needs to match exactly what is configured in the application code. For example, https and http register differently, and a mismatch would cause this error. The application ID/Client ID and tenant IDs also need to match in both places."