I have a problem with the synchronization of calendar with Google. I have an Ubuntu server on a local LAN that is running Odoo. I access Odoo in LAN through url

w3.mydomain.lan:8069 

And so far so good. Then I created a DynDNS domain and activated DNSS on my router to access it from the outside. I access it as

mydomain.office-on-the.net:8069 

It works perfectly. So I followed the instructions to synchronize the calendar with Google. I created the two values ​​required, Google Client ID and Client Secret Google, and I made sure they were well written without spaces or other garbage, and I enabled on the corresponding Google project the Google+ and Calendar APIs. I verified I did all correctly several times.

However, when I try to sync calendars, I get the following error:

400. That's an error. 
Error: invalid_request 
Invalid parameter value for redirect_uri: Non-public domains not allowed: 
w3.mydomain.lan/google_account/authentication 

However if I'm going to see the request, I get:

scope = https://www.googleapis.com/auth/calendar
response_type code =
redirect_uri = http://w3.mydomain.lan/google_account/authentication
access_type = offline
approval_prompt = force
state = {"s": "calendar", "d", "MioDominioERP", "f", "mydomain.office-on-the.net:8069/web#vi...nu_id=360&action=413"} 
client_id = xxx...xxx.apps.googleusercontent.com 

Why Google is able to see the internal domain name???

PS Obviously I specified redirect_uri in the Google project as

mydomain.office-on-the.net:8069/google_account/authentication

Thank you in advance.