[Plugin: Simple Google Connect] oauth2callback did not match a registered redirect URI

When I click on the login with Google button, I get the error

Error: redirect_uri_mismatch
The redirect URI in the request: https://www.mydomain.com/oauth2callback did not match a registered redirect URI

The problem, I think might be that

In my plugin settings, callback URL appears as
https://www.mydomain.com/oauth2callback
(with no opportunity to edit anything but the slug.

While in Google API Access, the callback URL appears as
https://www.mydomain.com/oauth2callback
with no opportunity to edit anything.

How do I reconcile the http v https difference?

https://www.ads-software.com/extend/plugins/simple-google-connect/