When buying a house, you must have a purchase invoice. When paying the down payment, the down payment invoice will be given, and the bank loan will be transferred to the developer. The remaining invoices will also be issued, and these two invoices will constitute the purchase invoice. Don't underestimate the paper for purchasing invoices. Without it, many things can't be accomplished. Without the purchase invoice, it is very troublesome to apply for a real estate license. Whether you run by yourself or act as an agent, the housing management department will require buyers to issue purchase invoices, which is an important certificate for the completion of housing transactions.