Hey @AceVla! No apologies necessary, thanks for providing the additional info!
That 403 response is new! Can you explain what changed from your original situation (with the 401 response) to cause this new behavior?
In terms of alternate methods of authentication: you should be able to use Basic authentication as an alternative to the API key. Details can be found here; tools like curl and Postman can generate that header automatically from your username/password. This will bypass the token entirely, and perform the request as the user themselves (as opposed to a snapshot of the user's roles/permissions in the case of the API token). Whether or not that method works should give us insight into where the problem is, here.
One more question in the meantime: is this user able to perform these cases workflows manually in the kibana UI?