[Solved] Google oAuth using Web API

Ahhhh… I have created 3 different credentials in the Google API dashboard, but I can’t seem to authorise.

No matter which credentials I use, I get error 401. The JSON result is:
{ "error" : "invalid_client", "error_description" : "Unauthorized" }

Any suggestions?
https://x.thunkable.com/projects/5dd4deea2acb250a941b289b/9f0a6441-92b5-4782-b7f8-7535fbe9417d/designer
(forgive its ugliness)