Hello @Lucas Klassmann ,
I would recommend you to raise a support case with Microsoft Graph, a Support Engineer will be able to assist you better. You can raise support ticket from
http://aad.portal.azure.com/ or https://admin.microsoft.com/#/support/requests.
I would also recommend you to refer to this similar posts: https://learn.microsoft.com/en-us/answers/questions/1190965/could-not-obtain-a-wac-access-token
Hope this helps.
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