Hi GFA,
PayPal will redirect back to the base URL and because the booking form is published in an iFrame PayPal can not detect the website URL that the iFrame is published on.
However, we are working to add your company's name and logo to the booking form so the customer is not confused when they only see the booking form on PayPal cancellation.
This has not been a problem so far but we are always working to make user experience better.

Hope this helps.
Kind regards.