If you set the attribute ‘block’ to true, a transparent background will be displayed behind the modal, blocking the scroll on the page, until the modal is closed.
index.html
<script>
    window.pactto = window.pactto || {};
    window.pactto.coach = 'username';
    window.pactto.company = 'Coach Name';
    // Add block attribute:
    window.pactto.block = true;
</script>