Hey, i just bought the msi z87m gaming motherboard and it has a rebate of 20$ to which i would like to apply. It has been straight-forward until it asked me the invoice/order # and the serial #. I easily found the invoice number on top of the order details, but i can't find the serial number. I tried to put the item number thinking that it was it, but it says "MSI product serial number is already attached to a Claim!" and i don't want to put the wrong one. Please Help!!! 🙁