Empty GUID error when using Azure AD consent flow

Question

I'm currently trying to integrate with Azure AD using the admin consent flow.
I've set up an app in our domain, set a few permissions on it and am then navigating to the following link:

https://login.microsoftonline.com/mytestdomain.onmicrosoft.com/oauth2/authorize?client_id=12345678-1234-1234-1234-123456789012&response_type=code&redirect_uri=http://example.com/responsehandler&resource=12345678-1234-1234-1234-123456789012&prompt=admin_consent&state=12345

(Some of the values here have been swapped out for "example" values)

When I navigate there I get asked to sign in, which I do using a different test domain into which I want to import the app.
After signing in I'm shown a list of all the permissions that the app needs (which appear to be correct), I click accept but then I get the following error:

AADSTS90002: Requested tenant identifier '00000000-0000-0000-0000-000000000000' is not valid. Tenant identifiers may not be an empty GUID.

I'm not sure where this empty GUID is coming from and after some searching I can't find any reference to what might be causing it.

Answer 1

Daniel Camargo's comment above seems to have done the trick.
When I navigated to the login.microsoftonline.com link I was logging in with the user that created the domain.
If I log in with a test admin user that I created it works as I'd want.