GoogleClientAPI redirect_uri_mismatch

[froot]

When trying to connect to Google I get:

Error 400: redirect_uri_mismatch

I think however that I did everything right in the Google Console
- setup the project
- enabled the desired API (google calendar)
- set up a Service Account 
- downloaded the Service Account JSON (correct format with type: service_account) and uploaded put in the module’s Authentication Config field.
- shared the calendar with the Service Account (permissions: Make changes and manage sharing)
- created an OAuth 2.0 Client ID (Web application, named “ProcessWire GoogleClientAPI”).
- added Authorized JavaScript origins
- Added Authorized redirect URIs like so: https://myspecificsite.com.ddev.site/admin/module/edit?name=GoogleClientAPI
- Noted the client_id and client_secret and entered them in the module’s Client ID and Client Secret fields.

Any ideas what I might be doing wrong? I doubt the error is that it's a local installation, I get the same error when it's on the live server.
All support I can find is just saying that the OAuth URI might mismatch, lacking a trailing slash or something but I think that's not the case either.

Thanks for help!

EDIT: I think the error could be that the module is making a OAuth request to
https://myspecificsite.com.ddev.site/admin/module/edit?name=GoogleClientAPI flowName=GeneralOAuthFlow
which is not what's defined in the Google Console nor can it be with the empty space in there. There should at least be a "&" before the "flowName" GET variable?

@ryan

Edited May 19 by froot