Hello Cameron River,
Thanks for your question.
Based on the error message, the access token being used is associated with the old tenant ID, but your subscription is now under a new tenant ID
You may need to sign out and sign in with credentials associated with the new tenant. You can test in an incognito browser to ensure no cached credentials
If you are using the CLI please use az login and sign in with the new tenant's tenant ID.
Regards,
You can mark it 'Accept Answer' if this helped.