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I think I see what you mean, but instead of an invoice, maybe you can contact the seller (or creator of the product) and have them send you a signed consent form or release form that verifies the product is free to use in your game? That might be even better than an invoice with $0? Assuming you just want it verifiable that the product is free to use. Unless this is for tax purposes or a financial reason, then ignore everything I just said. ;)
Basically yes but I was thinking if there would be a automatic system so the sellers dont have to do more work.
