Listing owner gets charged for editing and re-submitting their listing

Hi. I have set up the Pricing and Payments Add-on to work with Woocommerce and it works fine for new listings where if the listing owner chooses a package that is not free, on submission the package gets added to the checkout cart and the payment process proceeds with my selected payment gateway.

The problem I have is the same thing happens if the listing owner updates the listing details (of an existing listing whose membership package has already been paid for) and re-submits, the owner is again taken through a checkout process to pay for the listing. This means that listing owners cannot update their existing listings such as adding new photos or contact details without being charged again. How can I set things up that this does not happen. If a listing package has already been paid for and is active, I want the listing owner to be able to make changes to their listing without being charged again for it.