Is there a way to require user to select T-shirt size?

Hi,

I have checked your form, and I can see that you are referring to the product option inside the Product Settings, correct?

Unfortunately, it's not possible to require the Product Options inside the Payment field. However, you might want to use the Product List field: New Product List Form Field, in this way you can create a condition to require a field based on the user's answer, here's an example:

But this workflow, the option for the T-Shirt Size is added outside the Product List field.

For reference: How-to-Make-a-Field-Required-Based-on-User-s-Answer

Please feel free to clone this demo form for your reference: https://form.jotform.com/202685539942971

Let us know if you need further assistance.