Payment Form: why can't I duplicate this product section?

Are you referring to this form and section? https://www.jotform.com/90514231768154 

Unfortunately, duplicating payment fields is not possible, because there cannot be more than two payments fields in one form. If you want to allow users to make a new submission, you can add a Single Choice field to ask them if they want to make a new payment, and redirect them to the same form if the answer is yes. This is possible through conditions, please check this guide: 

https://www.jotform.com/help/317-Change-Thank-You-Page-URL-Based-on-a-Condition 

Let us know if you need more help.