Plugin shows but it doesn’t work

Hello, I have a problem that plugin doesn’t work inside. So far I have done this steps:
– install and activate a plugin
– insert WeTransfer API Key
– in Contact Forms 7 I used [ozpital-wpwetransfer]
– in Ozpital On success event I used default code:

// Get the CF7 field that we want to populate with a WeTransfer URL
var urlInputField = document.getElementById('wetransfer_url');

// Check that the CF7 field exists on the current page
if (urlInputField) {
    // Populate the CF7 field with the URL
    urlInputField.value = event.detail.url;
}

So at the moment with all this, it doesn’t work. It shows in CF7 but it doesn’t work as it should. What I am missing?
Also, I would suggest that installation manuals are more clear for users with less technical knowledge as I am 🙂

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