Error sending email using GMail SMTP

I get the following error message after 2 hours of sending a successful test email, what could be the issue? I followed everything as per the instruction. I use GMail Gsuite for my domain.

EMAIL DELIVERY ERROR: the plugin WP Mail SMTP v2.0.0 logged this error during the last time it tried to send an email:

Mailer: Gmail
{
“error”: {
“errors”: [
{
“domain”: “global”,
“reason”: “required”,
“message”: “Login Required”,
“locationType”: “header”,
“location”: “Authorization”
}
],
“code”: 401,
“message”: “Login Required”
}
}
Consider running an email test after fixing it.