Disabling plugin

I’m trying to disable the plugin using the code from this page:

https://codemiq.com/en/disable-wp-html-mail-template-for-specific-emails/

For emails with the subject “SMS. Here’s the snippet I’m using but it doesn’t seem to work.

add_filter( 'haet_mail_use_template', 'disable_email_template_by_subject', 10, 2 );
function disable_email_template_by_subject( $use_template, $email ){
    if( stripos( $email['subject'], 'SMS' ) !== false )
      $use_template = false;
  return $use_template;
}

Do you have any suggestion?

Thanks!