E-invoicing in Mexico is based on a clearance model which is named CFDI (Comprobante Fiscal Digital por Internet – Internet-based Digital Tax Invoice). Since 1st, 2018, the only valid version for CFDIs is version 3.3. However with the most recent update CDFI version 4.0 is mandatory from 1 Jan 2023. Firstly, taxpayers must obtain a Federal Taxpayer Registration from SAT. SAT should also provide taxpayers a unique electronic signature key (FIEL) and a digital stamp called a Certificado de Sello Digital (CSD). To validate and stamp invoices as they are issued, appoint a government-approved e-Invoicing firm (PAC). VAT returns which include information about sales and purchases, must be reported monthly.