Error trying to authorize Gmail API with WP Mail SMTP

Hi there,

I’m setting up SMTP for my wife’s website that’s hosted on WP. We originally used DreamHost but that wasn’t working, so have tried setting up connecting through the Gmail API.

We are running WP 5.7 and the latest version of the WP Mail SMTP plugin(v2.6.0). Upon advice from other threads, I deactivated and deleted the WP Mail SMTP plugin, reinstalled it, and then tried setting up the SMTP through Gmail from scratch.

I get the following error:

EMAIL DELIVERY ERROR: the plugin WP Mail SMTP v2.6.0 logged this error during the last time it tried to send an email:

Mailer: Gmail
{
"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"
}
}

I have validated that I’m using the correct Client ID and Client Secret from the Google API, so I don’t know what else to do.

Any help is much appreciated, TIA!!