wpcf7mailsent event not working on iPad

Don’t why I can’t get the wpcf7mailsent event sample code from the contact 7 form official website to work on my iPad air (both Chrome and Safari). Instead of showing a pop up, the address bar will show https://www.sonarpen.com/joinnow#wpcf7-f1529-p1453-o1 or o2 and the browser just turns blank and freeze.

The code works on desktop and mobile phone but not iPad. which is very strange. pls help. Thanks.

<script>
document.addEventListener( ‘wpcf7mailsent’, function( event ) {
alert( “Thanks!” );
}, false );
</script>

Elton

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