I want to add thank you page as a lightbox. how do i do that?

I have a form and after submit i want the thank you message to appear as a lightbox. Please let know how this can be done. Thanks

Unfortunately, this is not possible. We have our form thank you as a redirect page or URL. We have a request for this feature, but we don't have an update yet until this time. 

For the meantime, if you are after of showing the same form after submit, you can redirect your submitters to the same form or page. Just set it as your custom thank you URL.

https://www.jotform.com/help/38-Redirecting-Users-to-a-Different-Page