Hi.
I’ve followed the instruction and (for example):
Authorised JavaScript origins
For use with requests from a browser
URIs
https://example.com
Authorised redirect URIs
https://example.com?cmd=frappe.integrations.doctype.google_contacts.google_contacts.google_callback
All I am getting is Error 400: redirect_uri_mismatch. 
Facing the same issue. The issue is Frappe erpnext instructs to add the redirect url as : - [Example Domain ]
But the app when it sends request to googe it sends as - https://example.com:8000?cmd=frappe.integrations.doctype.google_contacts.google_contacts.google_callback)
This is causing the issue.
Did you solve it or anyone was able to correct this