Jason Hendriks on "[Plugin: WP Mail SMTP] SMTP Error: Could not authenticate."

["ErrorInfo"]=>
string(35) "SMTP Error: Could not authenticate."

An authentication error mean Google refused your name and password as a valid combination.

Either

1. Your name and password is wrong or
2. Google disabled your password auth capability due to suspicious activity and you'll have to use an app that supports 'Google's security standards' - i.e. OAuth 2.0