WordPress at a glance
function is not described

PHPMailer\PHPMailer

PHPMailer::isError() public WP 1.0

Check if an error occurred.

{} It's a method of the class: PHPMailer{}

No Hooks.

Return

true|false. True if an error did occur

Usage

$PHPMailer = new PHPMailer();
$PHPMailer->isError();

Code of PHPMailer::isError() WP 5.7.2

<?php
public function isError()
{
    return $this->error_count > 0;
}