The following error shows up when attempting to add a Google account to the desktop outlook app. All the instructions below on to resolve this issue. This solution has been tested twice and has worked successfully.
Step 1: Remove access for Microsoft Apps & Services in Gmail.
Close Outlook.
Sign in to your Google account on google.com.
Select your profile picture in the top corner and select Manage your Google Account.
On the left side menu, select Security.
Scroll down to Your connections to third-party apps & services and select Microsoft apps & services.
Locate Microsoft apps & services has some access to your Google Account and select See Details.
Under Access you’ve given to Microsoft apps & services, select Remove all access.
Select Confirm.
Step 2: Delete the Google IMAP credentials from Windows Credential Manager
From the Windows Start menu, search for Credential Manager and open it. On Windows 10 you may need to open the Control Panel to access Credential Manager. For more information, please go to Accessing Credential Manager.
Under Manage your credentials, select Windows Credentials.
Scroll down to Generic credentials and locate those starting with MicrosoftOffice16_Data:OAUTH2.
Expand each of these and hover over MicrosoftOffice16_Data:OAUTH2 until it shows the full name including the tp_google_imap_Oauth2. These are the Google credentials for your Gmail account.
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Select Remove for each of these with the MicrosoftOffice16_Data:OAUTH2. If you have multiple Gmail accounts, you will need to sign in to each of them again.
If you want to avoid removing Google IMAP credentials except for the specific affected account, you can map the credentials by comparing them to the identities in this registry key below. Open Registry Editor and paste this path in the Address bar at the top.
Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\IdentitiesThe sub keys to this registry key above include your Gmail identity. At the beginning of the identity registry key is a number that matches your Gmail credential in Credential Manager. See the examples below for reference.
After you have done the steps above you are now ready to Sign in via browser from Outlook. Open Outlook to the Outlook profile that was not syncing and select the Sign in via browser business bar in Outlook. Make sure during browser sign in to check the box for Microsoft apps & services noted at the top of this article.
If you removed the Gmail account from your Outlook profile, select File, Add account to add the Gmail account back again and do the browser sign in process again.