Edit Test Payment Form

Hello,
As I see Pricing Manager works based on listings, not users.
My site will be based on users buying a subscription, so they can add many listings.
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A workaround I thought to accomplish this is to create a pricing package, eg. silver = $10/m.
When user add listing he will pay for the 1st listing.

for the following ones, at the checkout, he could choose the “test payment” gateway
(I would call this “check here if you already paid the package”).

So he will end checkout process without any payment.
Then I will manually check that listing as PAID.
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Where can I edit the “test payment” form?
I would not want user need to fill the form over and over.
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If there is a better way to accomplish this, I’m all ears!!
I’m aware this is not so user-friendly

Thank you!!