Seller. When the seller collects the courier fee, it will charge the buyer the corresponding fee, which will be included in the sales as freight and other expenses, and then the invoice will be issued, so the seller will issue the invoice. Invoice refers to the business vouchers issued and collected by all units and individuals in buying and selling goods, providing or receiving services and engaging in other business activities. It is the original basis of accounting and an important basis for law enforcement inspection by audit institutions and tax authorities.