To edit the product subheadline text you first need to know how to create a product. Read this article to learn how to create a product in Cartfuel: How To Create A Product In Cartfuel?
Step 1: Edit The Product Subheadline
When you add a new product to your payment form toggle on the "Edit Product Subheadline Text" selector
Enter the desired text you want to appear under your product name in the input box. Example: Instead of "Billed Once" maybe you want to indicate the product has free shipping; you would enter "Free Shipping"
Click "Update" to save your changes