HTML widget not reading WePay.com Donate Button code

I’m using wordpress.com with the free Sundance Theme. I’m trying to paste code from WePay.com (a donate button) into the Text widget in my Sidebar. When I save the code, it shows up in the sidebar as the full code, not the image. I spoke with WePay, and they can’t think of anything on their end, and their code is accurate. What can I do?