'''Q: '''Have you already created an imap gmail account for email address with Authentication Method : Oauth2? '''Q: '''When setting up gmail mail account, did you get the prompt by a google pop up window to enter password etc and to select allow thunderbird to access server ? Not sure if the issue is creating the gmail address book OR you have already created it, but cannot add contacts to it. I use gmail, so I removed the address book and restarted a fresh using the following: To add gmail address book: * In Address Book * Click on the 'Create a new Address Book' icon - * select 'Add cardav Address Book' * Username - enter full gmail email address * Location is auto completed * click on 'Continue' * Select 'Address Book' if not selected * click on 'Continue' '''Q: '''Are you prompted by a google pop up window to enter password etc and to select allow thunderbird to access server ? 'Address book' is auto added in the list of Address Books. It auto displays any contact you already have in that online address book. * Click on the 3 dot icon, select 'Properties' * To edit name of address book - added the word Gmail so it says 'Gmail Address Book'. * check the 'Synchronise' checkbox is selected. * check the 'read only' is NOT selected. * click on 'OK' Added a Contact to gmail address book: * Select 'Gmail Address Book' * Click on '+Add Contact' button * Enter name, email address etc * check the 'Add to' is 'Gmail Address Book' * click on 'Save' '''Check for a saved oauth token:''' * In Settings > Privacy & Security * click on 'Saved Passwords' '''Q: '''Do you a line which looks like this: * oauth://accounts.google.com (https://www.googleapis.com/auth/carddav) '''Firewall:''' It's controlled by either the default that came with computer or by an Anti-Virus you installed. Access the Firewall and make sure the Thunderbird program is set up an allowed program. Don't disable Firewall as that does not help and another may auto function instead. You need the firewall to allow Thunderbird. '''VPN''' Have you enabled a VPN? Gmail does not like VPN. It cannot see your IP and thinks you might be a hacker. Some AV producys have a habit of auto enabling them. Switch it off.

Toad -Hall, thank you very much. Your 'to add gmail address book' instructions did the trick.