How to edit an invoice once it has been paid?

[RemnantsPlus]

I want to change the shipping charges on an invoice.  The buyer has already paid it and I intend to refund the overage.  

Cannot find a way to do it.  Any help out there?

[Quandary]

Not possible once it's been paid.

[Whac-A-Mole]

find the transaction and use the refund feature.

Paypal will refund its share as well.