Google Calendar does not connect

Dear all,

Google calendar authentication is requetsed via:

redirect_uri=http://domain.com:8000?cmd=frappe.integrations.doctype.google_calendar.google_calendar.google_callback flowName=GeneralOAuthFlow

when it should be:

redirect_uri=https://domain.com?cmd=frappe.integrations.doctype.google_calendar.google_calendar.google_callback flowName=GeneralOAuthFlow

Protocol https, port no port

site config json is:
“webserver_port”: 8000,
“root_url”: “https://domain.com”,
“host_name”: “domain.com

The bench listens on 8000, nginx is configured as a proxy:

location / {
proxy_pass http://127.0.0.1:8000/;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_redirect http://127.0.0.1:8000/ /;
}

what am I missing?

thanks a lot for your help,
Thomas