Invoicing Requirements in Mexico: The Complete List
The invoicing requirements in Mexico come down to five things: an active RFC, a valid e.firma, a Digital Seal Certificate (CSD), a tax regime correctly registered with the SAT, and access to a PAC — or the SAT's free tool — to stamp the receipt. Miss any one of these five and the CFDI simply cannot be issued, or the SAT rejects it. If you have never invoiced before, the confusing part usually isn't the technology — it's knowing in what order to get each requirement. That's exactly what this guide covers.
Before getting into the details, it helps to be clear on what the document itself is: if the CFDI concept is still new to you, start with our guide what is a CFDI?
RFC: The Mandatory Starting Point
The RFC (Registro Federal de Contribuyentes) is the tax ID that identifies you before the SAT, and the first requirement, with no exceptions, to be able to invoice. You get it when you register as an individual (persona física) or a legal entity (persona moral), and from that point on it's tied to your Constancia de Situación Fiscal — the document that summarizes your tax regime, fiscal address, and current obligations.
A common mistake among businesses that are just starting to invoice is using an RFC registered a while back but never updated: changes of address, regime, or economic activity that weren't reflected with the SAT end up causing CFDIs to be rejected months later, once the issuer or the recipient is working with outdated data.
e.firma: What It Is and What It's For
The e.firma (formerly known as FIEL) is your advanced electronic signature before the SAT. It's a personal cryptographic file, unique to each taxpayer, used to complete legally valid tax procedures online — including the process to obtain your Digital Seal Certificate.
The e.firma isn't used to stamp each individual invoice; its role is to authenticate you before the SAT and sign specific procedures, such as requesting your CSD. It's obtained in person at a SAT office with a scheduled appointment, and it has a limited validity period that must be renewed before it expires.
Digital Seal Certificate (CSD): The One That Signs Every Invoice
The CSD is the certificate that actually signs every CFDI you issue. Unlike the e.firma, which authenticates administrative procedures, the CSD is specific to electronic invoicing: every receipt you generate carries the digital seal produced with this certificate, which guarantees the document came from you and wasn't altered after it was issued.
To request your first CSD you need a valid e.firma. Once it's generated, the file is installed in your invoicing system or handed to your PAC so it can seal receipts on your behalf. The CSD also has a limited validity period and must be renewed; letting it expire without noticing is one of the most common reasons a business suddenly can't invoice from one day to the next.
Tax Regime and CFDI Use: The Data That Defines Every Invoice
These two SAT catalogs are mandatory on every CFDI, and they're usually the part that confuses first-time invoicers the most:
- Tax regime (régimen fiscal): defines under which scheme you pay taxes (for example, Régimen Simplificado de Confianza, Régimen General de Personas Morales, or Actividades Empresariales y Profesionales for individuals). It must match exactly the regime registered on the Constancia de Situación Fiscal — both yours as the issuer and your customer's as the recipient.
- CFDI use (uso de CFDI): indicates what the recipient will use that invoice for (acquisition of goods, general expenses, computer equipment, and many others). It must be compatible with the recipient's tax regime, or the receipt gets rejected during stamping.
Since CFDI 4.0, the recipient's name or legal name, postal code, and tax regime must match their Constancia de Situación Fiscal letter for letter. A stray space, a comma, or a different abbreviation is enough to make the stamping fail. The SAT only requires you to confirm those four data points — RFC, name or legal name, postal code, and tax regime — with your customer; you can ask for them or check them, but you cannot condition or refuse the invoice if the customer doesn't hand over the physical Constancia de Situación Fiscal. The CFF reform published in the DOF on November 7, 2025 and in force since January 1, 2026 made conditioning CFDI issuance on the customer showing their Constancia an infraction under Article 83, Section IX, punishable by fines of $21,420 to $122,440 MXN.
Individual vs. Legal Entity: What Changes When You Invoice
All five requirements — RFC, e.firma, CSD, tax regime, and PAC — apply equally to individuals (personas físicas) and legal entities (personas morales), but there are practical differences worth knowing:
- Individual / persona física (freelancers, independent professionals, small businesses): the RFC is generated from the CURP and usually includes a homoclave derived from your personal data. The most common tax regime for someone starting out is Régimen Simplificado de Confianza (RESICO) or Actividades Empresariales y Profesionales, depending on income level and activity type.
- Legal entity / persona moral (formally incorporated companies): the RFC is assigned to the legal name registered with a notary, and the e.firma and CSD are obtained in the company's name, typically through its legal representative. The typical tax regime is Régimen General de Personas Morales, though specific regimes exist for activities such as the primary sector or nonprofit organizations.
In both cases the technical invoicing process is identical once you have all five requirements in place; what changes is how the RFC, e.firma, and CSD are obtained, and which tax regime applies to your situation.
Choose a PAC to Stamp Your Invoices
No CFDI has fiscal validity without stamping (timbrado), and stamping is performed by a PAC (Proveedor Autorizado de Certificación) authorized by the SAT — or, for very low volumes, the SAT's own free tool, "Genera tu factura" (or the Factura SAT Móvil app). The PAC receives the XML signed with your CSD, validates its structure against the current catalogs, and, if everything checks out, adds the Timbre Fiscal Digital with the UUID folio that makes the receipt legally valid.
For businesses invoicing only a handful of times a month, the SAT's free tools may be enough. Once volume grows — recurring sales, integration with a point of sale, or an e-commerce platform — it's worth evaluating a PAC with its own API that lets you automate stamping instead of entering each invoice by hand.
Common Mistakes When Invoicing for the First Time
- Letting the CSD or e.firma expire without scheduling the renewal, which stops invoicing outright.
- Using the recipient's tax regime without confirming it with them, instead of validating the four current data points in writing — RFC, name or legal name, postal code, and tax regime — without conditioning the invoice on them handing over their Constancia de Situación Fiscal, a practice the SAT has penalized since the reform took effect on January 1, 2026.
- Pairing a CFDI use that's incompatible with the customer's tax regime, a frequent cause of rejection under CFDI 4.0.
- Not double-checking the recipient's fiscal postal code, which must match what's registered with the SAT, not necessarily the branch where the purchase happened.
- Invoicing manually once volume already justifies automation, which multiplies the risk of human error on every receipt.
If your business already issues several invoices a week, it's also worth reviewing our guide on electronic invoicing and the SAT for the full process from start to finish.
Frequently Asked Questions
Can I invoice without an e.firma?
Not to request your first CSD — the e.firma is required for that step. Once your CSD is installed in your invoicing system or your PAC's platform, stamping each subsequent invoice no longer requires the e.firma directly.
How long does it take to get an RFC and an e.firma?
The RFC can be obtained the same day through an in-person appointment with the SAT, and the e.firma is normally processed during that same appointment. Exact timing depends on appointment availability and the documentation you bring, so it's worth booking ahead.
What happens if the recipient's tax regime doesn't match what I entered on the invoice?
The PAC rejects the stamping and the CFDI is never generated. It's enough to confirm your customer's four current data points — RFC, name or legal name, postal code, and tax regime — instead of reusing old data; the SAT does not allow conditioning invoice issuance on the customer handing over their physical Constancia de Situación Fiscal.
Do I still need a PAC if I already have my CSD?
Yes. The CSD lets you sign the XML, but stamping — the step that gives the receipt fiscal validity — can only be performed by a SAT-authorized PAC, or by the SAT's own free tools for low volumes.
Do the invoicing requirements differ between an individual and a legal entity?
The five requirements are the same, but the process for each one differs: a legal entity's RFC is tied to its registered legal name rather than an individual CURP, and its e.firma and CSD are managed through the company's legal representative.
If your business needs to automate CFDI 4.0 issuance — from CSD management to direct integration with a PAC and your sales system — at AISDC we build custom CFDI invoicing solutions that remove manual data entry and cut the risk of rejection from incorrect data.