I am having a similar problem, would appreciate any advice
Versions:
WordPress: 4.9.1
WordPress MS: No
PHP: 7.0.21
WP Mail SMTP: 1.2.2
Params:
Mailer: gmail
Constants: No
Client ID/Secret: Yes
Auth Code: No
Access Token: No
Server:
OpenSSL: Yes
PHP.allow_url_fopen: Yes
PHP.stream_socket_client(): Yes
PHP.fsockopen(): Yes
PHP.curl_version(): Yes
Debug:
Error while sending via Gmail mailer: { “error”: { “errors”: [ { “domain”: “global”, “reason”: “required”, “message”: “Login Required”, “locationType”: “header”, “location”: “Authorization” } ], “code”: 401, “message”: “Login Required” } }