Hi guys
Wanted to let you know the follow post fixed it for me.
You will need to have an external URL linked to your HA, also in my case I have an SSL certificate.
Both configured using the Duck DNS add-on.
After which I changed the Redirection URL in my Google Cloud Project:
Step 6: Add the following URI (substitute your domain name): https://yourdomainname.com/auth/external/callback)
Once done I could enable the Nest integration by entering my Google Cloud Project ID when prompted by HA.