The billing system has records. Every invoice issued by the taxpayer will be uploaded to the tax system. If taxpayers issue invoices that are inconsistent with their own business, it is easy to compare them with big tax data. Taxes can also be compared with the expenses incurred by enterprises through third-party surveys such as banks, industry and commerce, so that they can be found and personal invoices can be found. 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 it is also an important basis for law enforcement inspection by audit institutions and tax authorities.