If you have online payments enabled for your online forms, you can add product items to your form and then set one or more of them to be mandatory (required). This means people must select that product item (or one product from a group of mandatory items) before they can submit your form.
To make a specific product mandatory, tick the Required checkbox beside the product.
Please see these related support articles:
- Add products or payments to a form.
- Automatically trigger selection of product (if you have triggers enabled, you can set a trigger against the product so that when a question is answered above in the form, the product is automatically selected and unable to be unselected unless the question is answered by a different answer.
- How to set a form to decline submission if payment unsuccessful ('No pay, No play').