Post SMTP stopped working using Gmail

Hello, I successfully installed and connected to my gmail account with emails getting through. It is now not sending emails through once again and I’m not sure of the root cause. As I am a business, emails from customers are important. Any help appreciated! Here is the error message:

{ “error”: { “code”: 401, “message”: “Request is missing required authentication credential. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.”, “errors”: [ { “message”: “Login Required.”, “domain”: “global”, “reason”: “required”, “location”: “Authorization”, “locationType”: “header” } ], “status”: “UNAUTHENTICATED”, “details”: [ { “@type”: “type.googleapis.com/google.rpc.ErrorInfo”, “reason”: “CREDENTIALS_MISSING”, “domain”: “googleapis.com”, “metadata”: { “method”: “caribou.api.proto.MailboxService.SendMessage”, “service”: “gmail.googleapis.com” } } ] } }

Thanks, Dan.