Sometimes a form is sent twice when the user fills it out once. Could this be because they are using a smartphone?

Hi HessAcademy,

Thank you for contacting Support.

One possible reason is that when the user reloads the submission page, it triggers another submission which causes a duplicate.

What I would suggest you try is the unique submission feature https://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form.

Let us know if you need further assistance.