I integrated:

<iframe id="ZSubscriptions" style="border: none;" src=" https://subscriptions.zoho.eu/subscribe//LIBUKB-1" width="700" height="900"><span data-mce-type="bookmark" style="display: inline-block; width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span></iframe><script type='text/javascript' src=' https://legalinabox.co.uk/wp-content/plugins/zoho-subscriptions/assets/js/zs-height-custom.js'></script>

into a page.

The content doesn´t show up at all. The plugin found the Plan correctly.

When test the basic URL in Set-up plans the link works correctly.

The error code in console is:

Refused to display ' https://subscriptions.zoho.eu/home' in a frame because it set 'X-Frame-Options' to 'deny'.