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.
I assumed that you are referring to this form (https://www.jotform.com/70635536504354). I checked the form and I noticed that multiple checkboxes are not visible to the form because it has a white background.
I cloned your form and add a color scheme, and I was now able to select from the options in the multiple checkbox field. Here's the result:
If you have other concerns, please let us know.