Still gives 400 error, screen 1001
Step by step again:
1. I went and created a new project, screen 1002 and 1003
here:
https://console.cloud.google.com/apis/dashboard?project=YOUR PROJECT NAME
2. I went to the libraries, activated api calendar, screenshots 1004 1005 1006
3. I went to Credential and created an oAuth client, screen 1007 with settings 1008
4. Registered in the OneBox application settings, screen 1009
5. On the oAuth consent screen tab, this is how it is now displayed, screen 1010