Billing and CFDI

Overview

Luis IT Repair includes built-in support for Mexican CFDI (Comprobante Fiscal Digital por Internet) electronic invoicing. This guide covers:

CFDI 4.0 configuration
SAT catalog integration
PAC (Proveedor Autorizado de Certificacion) setup
Invoice generation and stamping
Folio management
Tax compliance

This feature requires valid RFC, digital certificates (CSD), and a PAC provider contract.

CFDI Basics

What is CFDI?

CFDI (Comprobante Fiscal Digital por Internet) is Mexico’s electronic invoicing standard mandated by SAT (Servicio de Administracion Tributaria). It replaces paper invoices and is legally required for:

B2B transactions
B2C transactions over $2,000 MXN
Any transaction where the customer requests an invoice

CFDI 4.0 Structure

A CFDI includes:

Emisor (Issuer): Your business information
Receptor (Receiver): Customer information
Conceptos (Line Items): Products/services sold
Impuestos (Taxes): IVA, ISR, etc.
Complementos (Complements): Additional data (optional)
Sello Digital (Digital Stamp): Cryptographic signature
Timbre Fiscal Digital (SAT Stamp): PAC validation

Configuration

Enable Billing Module

Navigate to POS Settings

Go to Configuracion > POS y Facturacion > Facturacion

Enable Invoicing

Check the box:

☑ Habilitar facturacion en POS

Select Emission Mode

Choose how invoices are issued:

Ticket y factura: Print both receipt and invoice
Factura bajo solicitud: Invoice only when customer requests
Solo factura: Always invoice (no receipt)

Issuer Information (Emisor)

Your business legal name as registered with SATExample: "Servicios Tecnologicos Luis IT Repair S.A. de C.V."

rfcEmisor

string

required

Your business RFC (Tax ID)Format:

Persona Moral: 12 characters (e.g., ABC123456D01)
Persona Fisica: 13 characters (e.g., XAXX010101000)

This must match your SAT registration exactly.

regimenFiscal

string

required

Your tax regime code from SAT catalogCommon values:

601: General de Ley Personas Morales
612: Personas Fisicas con Actividades Empresariales y Profesionales
626: Regimen Simplificado de Confianza

Full SAT Catalog c_RegimenFiscal

codigoPostalEmisor

string

required

Your fiscal domicile postal code (5 digits)Example: "06000"

Series and Folio

serie

string

default:"A"

Invoice series identifier (up to 8 alphanumeric characters)Examples: "A", "FAC", "2024"

Use different series for different purposes (e.g., “A” for retail, “B” for wholesale).

folioActual

number

default:"1"

Current folio number (auto-increments with each invoice)Format: 6-digit padded (e.g., 000001, 000002)

autoIncrement

boolean

default:"true"

Automatically increment folio after successful invoice creation

Full Folio Format: {serie}-{folio} Examples:

A-000001
FAC-000123
2024-001500

CFDI Defaults

Uso de CFDI (Customer Use)

usoCFDI

string

default:"G03"

How the customer will use the invoiceCommon values:

G01: Adquisicion de mercancias
G02: Devoluciones, descuentos o bonificaciones
G03: Gastos en general (most common for retail)
I01: Construcciones
I02: Mobilario y equipo de oficina por inversiones
I03: Equipo de transporte
S01: Sin efectos fiscales

Full SAT Catalog c_UsoCFDI

Payment Method (Metodo de Pago)

metodoPago

string

default:"PUE"

Payment timing

PUE: Pago en Una sola Exhibicion (single payment)
PPD: Pago en Parcialidades o Diferido (installment payments)

Use PUE for immediate payments, PPD for credit sales requiring payment complements.

Payment Form (Forma de Pago)

formaPago

string

default:"01"

Payment instrument usedCommon values:

01: Efectivo (cash)
02: Cheque nominativo
03: Transferencia electronica de fondos
04: Tarjeta de credito
28: Tarjeta de debito
99: Por definir (use with PPD method)

Full SAT Catalog c_FormaPago

Customer Requirements

requiereRFCCliente

boolean

default:"true"

Require customer RFC before generating invoice

Legally required for all CFDI. Use XAXX010101000 for general public only when allowed.

requiereCorreoCliente

boolean

default:"false"

Require customer email to send invoice XML and PDF

Highly recommended for customer convenience and record-keeping.

Test Mode

timbradoPruebas

boolean

default:"true"

Enable test/sandbox modeWhen enabled:

Invoices are not legally valid
No real stamping/timbrado occurs
No charges from PAC
Testing CFDI generation workflow

Disable in production to issue legally valid invoices.

PAC Integration

What is a PAC?

A PAC (Proveedor Autorizado de Certificacion) is an SAT-authorized provider that validates and stamps (timbra) your CFDI with the official SAT seal. Popular PAC providers:

Finkok
SW Sapien
Facturomatic
Grupo Edicom
Paquetexpress

Setup Process

Choose a PAC Provider

Research and select a PAC provider based on:

Pricing per stamp
API quality and documentation
Support and reliability
Integration options

API endpoint URLs
Authentication credentials (API key, username/password)
Testing/sandbox credentials

Install PAC SDK or Library

Many PACs provide SDKs for Node.js:

npm install @finkok/sdk
# or
npm install sw-sapien-sdk

Configure Environment Variables

Add PAC credentials to your environment:

# In your .env file (never commit this!)
PAC_API_URL=https://api.pac-provider.com
PAC_API_KEY=your-api-key
PAC_USERNAME=your-username
PAC_PASSWORD=your-password

For Firebase Functions:

firebase functions:config:set \
  pac.api_url="https://api.pac-provider.com" \
  pac.api_key="your-api-key" \
  pac.username="your-username" \
  pac.password="your-password"

Implement Stamping Function

Create a Cloud Function to handle CFDI stamping:

functions/src/cfdiStamping.ts

import { onCall } from "firebase-functions/v2/https";
import * as admin from "firebase-admin";
// Import your PAC SDK

export const stampCFDI = onCall(async (request) => {
  const { cfdiXml, issuerRFC } = request.data;

  // Validate request
  if (!request.auth) {
    throw new Error("Authentication required");
  }

  try {
    // Call PAC API to stamp CFDI
    const response = await pacProvider.stamp({
      xml: cfdiXml,
      rfc: issuerRFC
    });

    // Store stamped CFDI in Firestore
    await admin.firestore()
      .collection('facturas')
      .add({
        folio: response.folio,
        uuid: response.uuid,
        xml: response.stampedXml,
        pdf: response.pdfUrl,
        createdAt: admin.firestore.FieldValue.serverTimestamp()
      });

    return {
      success: true,
      uuid: response.uuid,
      stampedXml: response.stampedXml,
      pdfUrl: response.pdfUrl
    };
  } catch (error) {
    console.error('PAC stamping error:', error);
    throw new Error('Failed to stamp CFDI');
  }
});

CFDI Generation Flow

Collect Invoice Data

From POS transaction:

Issuer information (from config)
Customer RFC and name
Line items (products/services)
Taxes (IVA)
Payment method and form
Uso de CFDI

Build CFDI XML

Generate XML according to SAT CFDI 4.0 schema:

<?xml version="1.0" encoding="UTF-8"?>
<cfdi:Comprobante
  xmlns:cfdi="http://www.sat.gob.mx/cfd/4"
  Version="4.0"
  Serie="A"
  Folio="000001"
  Fecha="2024-03-06T15:30:00"
  FormaPago="01"
  MetodoPago="PUE"
  TipoDeComprobante="I"
  Exportacion="01"
  LugarExpedicion="06000"
  SubTotal="1000.00"
  Total="1160.00">
  
  <cfdi:Emisor
    Rfc="ABC123456D01"
    Nombre="Luis IT Repair"
    RegimenFiscal="626"/>
  
  <cfdi:Receptor
    Rfc="XAXX010101000"
    Nombre="Cliente General"
    DomicilioFiscalReceptor="06000"
    RegimenFiscalReceptor="616"
    UsoCFDI="G03"/>
  
  <cfdi:Conceptos>
    <cfdi:Concepto
      ClaveProdServ="43211500"
      Cantidad="1"
      ClaveUnidad="E48"
      Descripcion="Reparacion de laptop"
      ValorUnitario="1000.00"
      Importe="1000.00"
      ObjetoImp="02">
      
      <cfdi:Impuestos>
        <cfdi:Traslados>
          <cfdi:Traslado
            Base="1000.00"
            Impuesto="002"
            TipoFactor="Tasa"
            TasaOCuota="0.160000"
            Importe="160.00"/>
        </cfdi:Traslados>
      </cfdi:Impuestos>
    </cfdi:Concepto>
  </cfdi:Conceptos>
  
  <cfdi:Impuestos
    TotalImpuestosTrasladados="160.00">
    <cfdi:Traslados>
      <cfdi:Traslado
        Base="1000.00"
        Impuesto="002"
        TipoFactor="Tasa"
        TasaOCuota="0.160000"
        Importe="160.00"/>
    </cfdi:Traslados>
  </cfdi:Impuestos>
</cfdi:Comprobante>

Sign XML with CSD

Apply your digital certificate (Certificado de Sello Digital):

Load .cer and .key files
Generate cryptographic seal
Add seal to XML

Send to PAC for Stamping

Submit signed XML to PAC API for validation and stamping.

Receive Stamped CFDI

PAC returns:

UUID (Folio Fiscal) - Unique SAT identifier
Timbre Fiscal Digital (SAT stamp)
Stamped XML with complete CFDI
Optional: PDF representation

Store and Deliver

Save to Firestore (facturas collection)
Send XML and PDF to customer via email
Print confirmation receipt
Update folio counter

SAT Catalogs

Common Catalog Codes

{
  "43211500": "Computer repair and maintenance services",
  "43211501": "Computer hardware installation services",
  "43211503": "Software installation services",
  "43211902": "Data recovery services",
  "43222600": "Software licensing services",
  "81112100": "Computer accessories",
  "81161700": "Data cables"
}

Full SAT Catalog Codes

Cancellation and Credits

Cancel Invoice

To cancel a CFDI:

Request Cancellation from PAC

Call PAC API with UUID to cancel:

const result = await pacProvider.cancelCFDI({
  uuid: 'ABC12345-6789-...',
  rfc: 'ABC123456D01',
  motive: '01', // Comprobante emitido con errores
  replacementUuid: null // Optional replacement UUID
});

Update Firestore Record

Mark invoice as cancelled:

await admin.firestore()
  .collection('facturas')
  .doc(invoiceId)
  .update({
    status: 'cancelled',
    cancelledAt: admin.firestore.FieldValue.serverTimestamp(),
    cancellationMotive: '01'
  });

Notify Customer

Send cancellation notification via email.

Credit Notes (Egreso)

For returns or corrections, create a credit note (Egreso CFDI):

<cfdi:Comprobante
  TipoDeComprobante="E"
  ...>
  <!-- References original invoice -->
</cfdi:Comprobante>

Compliance and Best Practices

Always Request Customer RFC

For legal compliance, always request customer RFC when issuing invoices. Only use “XAXX010101000” (general public) when legally allowed.

Backup Stamped XML Files

SAT requires you to keep XML files for 5 years. Implement automatic backup to cloud storage:

import { getStorage } from "firebase-admin/storage";

const bucket = getStorage().bucket();
await bucket.file(`facturas/${uuid}.xml`).save(stampedXml);

Monitor PAC Credits

Track your PAC credit balance to avoid service interruptions.

Test in Sandbox First

Always test CFDI generation in PAC sandbox before going live.

Validate XML Schema

Use SAT’s official XSD schemas to validate XML before sending to PAC.

Handle Cancellations Within 72 Hours

SAT rules allow easier cancellation within 72 hours of issuance.

Troubleshooting

PAC Rejects XML

Common causes:

Invalid RFC format
Incorrect catalog codes
Missing required fields
XML schema validation errors
Math errors in totals/taxes

Check PAC error response for specific validation failure.

Certificate Issues

Verify .cer and .key files are valid and not expired
Ensure CSD password is correct
Check that RFC in certificate matches configuration

UUID Not Generating

Verify PAC credentials are correct
Check PAC service status
Ensure you have sufficient PAC credits
Review PAC API logs

Customer Cannot Validate Invoice

Customers can validate invoices at: https://verificacfdi.facturaelectronica.sat.gob.mx/They need:

UUID
Issuer RFC
Receiver RFC
Total amount

Resources

SAT CFDI Portal

Official SAT documentation and catalogs

SAT Schemas

XML Schema Definition (XSD) files

CFDI Validator

Validate issued invoices

Authorized PAC List

SAT-authorized PAC providers

Next Steps

POS Settings

Configure IVA and ticket printing

Firebase Functions

Deploy billing functions

Get Started

Core Features

Guides

Configuration

Overview

CFDI Basics

What is CFDI?

CFDI 4.0 Structure

Configuration

Enable Billing Module

Issuer Information (Emisor)

Series and Folio

CFDI Defaults

Uso de CFDI (Customer Use)

Payment Method (Metodo de Pago)

Payment Form (Forma de Pago)

Customer Requirements

Test Mode

PAC Integration

What is a PAC?

Setup Process

CFDI Generation Flow

SAT Catalogs

Common Catalog Codes

Cancellation and Credits

Cancel Invoice

Credit Notes (Egreso)

Compliance and Best Practices

Troubleshooting

Resources

SAT CFDI Portal

SAT Schemas

CFDI Validator

Authorized PAC List

Next Steps

POS Settings

Firebase Functions

Build docs developers (and LLMs) love

Get Started

Core Features

Guides

Configuration

​Overview

​CFDI Basics

​What is CFDI?

​CFDI 4.0 Structure

​Configuration

​Enable Billing Module

​Issuer Information (Emisor)

​Series and Folio

​CFDI Defaults

​Uso de CFDI (Customer Use)

​Payment Method (Metodo de Pago)

​Payment Form (Forma de Pago)

​Customer Requirements

​Test Mode

​PAC Integration

​What is a PAC?

​Setup Process

​CFDI Generation Flow

​SAT Catalogs

​Common Catalog Codes

​Cancellation and Credits

​Cancel Invoice

​Credit Notes (Egreso)

​Compliance and Best Practices

​Troubleshooting

​Resources

SAT CFDI Portal

SAT Schemas

CFDI Validator

Authorized PAC List

​Next Steps

POS Settings

Firebase Functions

Build docs developers (and LLMs) love

Overview

CFDI Basics

What is CFDI?

CFDI 4.0 Structure

Configuration

Enable Billing Module

Issuer Information (Emisor)

Series and Folio

CFDI Defaults

Uso de CFDI (Customer Use)

Payment Method (Metodo de Pago)

Payment Form (Forma de Pago)

Customer Requirements

Test Mode

PAC Integration

What is a PAC?

Setup Process

CFDI Generation Flow

SAT Catalogs

Common Catalog Codes

Cancellation and Credits

Cancel Invoice

Credit Notes (Egreso)

Compliance and Best Practices

Troubleshooting

Resources

Next Steps