SMTP email application stopped working

We have an online php booking system (www.quantumwaste.com/app) that has been working for several years. On the first of April 2022 the application's email service stopped working. For example, when a new customer signs up they do not receive the confirmation email to validate their email address. Another example is that customers do not receive the email with the invoice when the work is completed. We had not made any changes to the applciation for months so that is not causing the problem. Maybe some updates or missing updates are causing the problem?

We would need somebody to access our server to trouble shoot this problem and restore the email service.

Thank you for your interest. We hope that you can help us.

Note: While we do not know what is causing the problem below is a cut and paste of the application email credentials for your reference:

function senVerificationLink( $email, $pass, $name) {
$link="Click To Reset passwordSend())