When trying to authorize or re-authorize a Gmail Connector in Workflows, a 403 Error is received after clicking Continue, and the Gmail Connector is not set up correctly. Here is what the full error may look like:
 

{
    "error": {
        "code": 403,
        "message": "Request had insufficient authentication scopes.",
        "errors": [
            {
                "message": "Insufficient Permission",
                "domain": "global",
                "reason": "insufficientPermissions"
            }
        ],
        "status": "PERMISSION_DENIED",
        "details": [
            {
                "@type": "type.googleapis.com/google.rpc.ErrorInfo",
                "reason": "ACCESS_TOKEN_SCOPE_INSUFFICIENT",
                "domain": "googleapis.com",
                "metadata": {
                    "service": "gmail.googleapis.com",
                    "method": "caribou.api.proto.MailboxService.GetProfile"
                }
            }
        ]
    }
}

• Workflows
• Gmail Connector 
  • initial Setup
  • re-authorization

The necessary permissions (scopes) were not granted when setting up the Gmail Connector in the Workflows Console. This action occurs after selecting the Google Account when setting up the Gmail Connector.

In Workflows Console > Connections:

1. Create a New Connection for Gmail (or re-authorize the existing connection encountering the error).
2. Select or enter the Google account to associate with the connection.
3. On the following screen, Select All items to grant permission to all the necessary items.

4. Press Continue.

Related References

• Gmail Connector - Authorization