what is Transfer ID ?

They probably meant Transaction IDs. And that is the receipt number for purchase of ZP. You purchase ZP with your credit/debit card, or a prepaid game card like UGC for example, and a receipt is emailed to the email you provide at the time of deposit.

You should be keeping those receipts as
A) proof-of-purchase in case one didn't get their zp
and
proof of ownership of an account because of purchasing ZP.

So in a nutshell, buy some ZP, get an email from the sellers, and with TWO transactions like that you can display those transaction IDs to aid you in getting your security answer.