When the Youform is embedded in your website as an iframe, because of browser security policy, it will not automatically redirect. You'll need to add the following code on your page to handle the redirect:
<script>
window.addEventListener('message', function(event) {
if (event.data && event.data && event.data.name == 'youformRedirect') {
window.location.href = event.data.url
}
});
</script>
You can add this code at the bottom your page before closing the </body>
tag.