Failed to authenticate with Google

Solution 1:

I too had the exact same issue with Apple's Mail app as you described. Suddenly both my Gmail accounts asked me to re-authenticate. For both accounts I got the "Failed to authenticate with Google" message after entering my passwords. Removing and adding an account gave the same failure message. But every time I authenticated in Safari I got an email from Google saying I've successfully authenticated MacOS. That got me thinking that the issue must be on the Apple side.

The solution that worked for me was:

1. Open the application "Keychain Access"
2. Look for application passwords containing the words "gmail" or "google"
3. Remove all the entries you find and reboot
4. Authenticate or re-add your Google account

Solution 2:

I had this same issue now, I think. I had updated the password for my gmail account and needed to re-authenticate the Google account in Mac OS. When I went into System Preferences > Internet Accounts I got a dialog saying I needed to re-authenticate and when I clicked the "Open Safari" button in the dialog I just got an error message saying Failed to authenticate with Google.

Solution was to restart my computer, after that it worked just fine.

(I also set my default browser to Safari as recommended on reddit but that didn't help before the restart so I don't think it helped at all)