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.
If you are adding your form via a link using non-HTTPS connection, this could be the cause. Facebook often block external contents for security reason even they are safe sometimes.
I would suggest you use the Publish option from form builder to add your form to Facebook - http://www.jotform.com/help/22-Adding-Form-to-Facebook-Pages.