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.
This was caused by the theme of your submit button and the logo you have added to your jotform.
It seems that it was being loaded over HTTP instead of HTTPS causing this to you.
The best way to fix it is to go to injected CSS styles and search for all entries with http:// and replace them with https:// or better yet with just //.
I have just done this for you so that you will not have to do it on this jotform.