What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
It's not a bug. But that is because of your incomplete custom thank you page URL. You are using:
Without the HTTP or HTTPS protocol, that would show you an error in the page.
You should put:
But this page doesn't exist in your website.
Please correct it by clicking the "Change Page Link" button in the thank you wizard: