Javascript not firing

Trying to push to GTM dataLayer and both of the following do not fire:

document.addEventListener( 'wpcf7mailsent', function( event ) {

        dataLayer.push({

          'event' : 'wpcf7successfulsubmit',

          'formId': event.detail.contactFormId

  })

 });

OR

dataLayer.push({

          'event' : 'wpcf7successfulsubmit',

          'formId': event.detail.contactFormId

 });

The page I need help with: [log in to see the link]