You don't need an invoice upstairs, just a sales voucher. That is to say, there is no problem with receipts and the like, and there is no need to add money to invoice.

Don't worry about the paperwork, it's not that troublesome. When you need a warranty, you can directly mail all the headphones, warranty cards and receipts (see which is closest to you, Guangzhou or Beijing). Leave your contact information (phone number, address, etc.). ) and damage and so on. The postage is only paid in the past, and the other party will pay it when you come back.