EMAIL DELIVERY ERROR logged by WPMailSMTP v1.5.2

Can someone tell me what causes the following issue, and how to fix it if you’re not a programmer?

It indicates that I am supposed to review my WP Mail SMTP settings, but I have no idea what to check for – everything was done per the instructions, and I wouldn’t be able to tell if something is “wrong” based on the code provided.

Hints and help appreciated. ??

***
EMAIL DELIVERY ERROR: the plugin WP Mail SMTP v1.5.2 logged this error during the last time it tried to send an email:
Mailer: Gmail
{
“error”: {
“errors”: [
{
“domain”: “global”,
“reason”: “failedPrecondition”,
“message”: “Bad Request”
}
],
“code”: 400,
“message”: “Bad Request”
}
}
***