paypal invoice is exactly what is sounds like. Its an invoice sent through paypal. lol. You can buy things cheaper that way because you are buying off eBay. So the seller only has to pay PP fees instead of both PP and Ebay fees as they normally would. You are still protected as a buy from the exact same buyer protection that eBay has because PP and Ebay are owned by the same company and both have the same buyer protection policy. Its the way you would buy anything from anyone here on denimblog or SUFU marketplace. You just need to ensure that the name of the item and description of the item is listed in the invoice and it is marked as goods and not "gift".
Oh thanks. Didn't even know such thing exists. I just use PayPal like a credit card. I'm such a good scam candidate. Sometimes I send PayPal remit first without any kind of invoice.