Once your setup all the field on the form drag and drop the pay button to the form body. Click on the edit and it will prompt you with the widget designer.
From the widget designer, you can set the button text, Product name prefix, ID of the attribute, Total price attribute, what action need to take once the form is submitted, update the status option.
It also allows you to restrict payment for specific statuses. Once you finish configure the widget click on save.