How do I make a working form in a template?

Hi, I feel this is super newby, but I can’t figure it out. I tried using a simple html form in one of my templates, it just has a submit button that you push with the goal of it outputting a slot machine roll for a game. However, when I click the button I get this error: ◾ This form has expired. Please refresh and try again.

I’ve searched and tried everything I can think of, including being sure my server and EE are set to the same time zone. Any ideas are appreciated. Thanks.