SAT Validation

Overview

SMAF implements comprehensive validation mechanisms to ensure all CFDI invoices comply with SAT (Servicio de Administración Tributaria) requirements. The system validates UUIDs, prevents duplicate submissions, verifies RFC formats, and ensures tax compliance.

UUID Validation

The UUID (Universally Unique Identifier) is the fiscal folio assigned by the SAT’s authorized certification provider (PAC). SMAF validates UUIDs to prevent fraud and duplicate submissions.

UUID Structure

Valid UUIDs follow the RFC 4122 format:

12345678-1234-1234-1234-123456789012

Duplicate Detection for Expense Reports

The system checks if a UUID has already been registered in the expense reporting system:

public static string Exist_UUUID(string psUUID)
{
    string resultado = "";
    
    // Query the expense verification table
    string Query = "SELECT CLV_DOC FROM crip_comision_comprobacion ";
    Query += " WHERE CLV_DOC= '" + psUUID + "' AND ESTATUS IN ('1','5','7')";
    
    MySqlConnection ConexionMysql = MngConexion.getConexionMysql();
    MySqlCommand cmd = new MySqlCommand(Query, ConexionMysql);
    cmd.Connection.Open();
    MySqlDataReader Reader = cmd.ExecuteReader();
    
    if (Reader.Read())
    {
        // UUID already exists in the system
        resultado = Convert.ToString(Reader["CLV_DOC"]);
    }
    
    MngConexion.disposeConexionSMAF(ConexionMysql);
    return resultado;
}

Duplicate Detection for Direct Payments

For direct ministry payments (ministraciones), a separate validation ensures UUIDs aren’t reused:

public static string Exist_UUUID_Ministracion(string psUUID)
{
    string resultado = "";
    
    string Query = "SELECT DOCUMENTO AS DOCUMENTO ";
    Query += "FROM crip_ministracion";
    Query += " WHERE DOCUMENTO = '" + psUUID + "'";
    Query += " AND ESTATUS != '0'";
    
    MySqlConnection ConexionMysql = MngConexion.getConexionMysql();
    MySqlCommand cmd = new MySqlCommand(Query, ConexionMysql);
    cmd.Connection.Open();
    MySqlDataReader Reader = cmd.ExecuteReader();
    
    if (Reader.Read())
    {
        resultado = Convert.ToString(Reader["DOCUMENTO"]);
    }
    
    MngConexion.disposeConexionSMAF(ConexionMysql);
    return resultado;
}

Validation Flow

RFC Validation

RFC (Registro Federal de Contribuyentes) is the Mexican tax identification number. SMAF validates RFC formats for both individuals and legal entities.

RFC Format Rules

Legal Entities (Personas Morales):

12 characters
Format: AAA010101ABC
First 3 characters: Alphabetic (company initials)
Next 6 characters: Date (YYMMDD)
Last 3 characters: Alphanumeric (homoclave)

Individuals (Personas Físicas):

13 characters
Format: AAAA010101ABC
First 4 characters: Alphabetic (name initials)
Next 6 characters: Date (YYMMDD)
Last 3 characters: Alphanumeric (homoclave)

RFC Extraction

RFC values are extracted from both issuer and receiver data:

// Extract issuer RFC
poXml.RFC_EMISOR = factura.Emisor.Rfc;

// Extract receiver RFC
poXml.RFC_RECEPTOR = factura.Receptor.Rfc;

RFC Storage in Database

The system stores RFC data in multiple tables:

public static bool Inserta_DetalleXML(
    string psUsuario, 
    string psUbicacion,
    string psDocumento, 
    string psXml,
    string psTimbreFiscal,
    string psProvedor,  // RFC of provider
    string psConcepto,
    string psPartida,
    // ... additional parameters
)
{
    string Query = "INSERT INTO crip_xml_detalle (";
    Query += " UUID,";
    Query += " RFC,";  // Provider's RFC
    // ... other fields
    
    Query += " VALUES (";
    Query += " '" + psTimbreFiscal + "',";  // UUID
    Query += " '" + psProvedor + "',";      // RFC
    // ... other values
}

Invoice Verification Process

The complete invoice verification workflow ensures compliance at multiple levels:

Step 1: XML Structure Validation

try
{
    XmlSerializer serializer = new XmlSerializer(typeof(Comprobante));
    XmlTextReader reader = new XmlTextReader(psArchivo);
    Comprobante factura = (Comprobante)serializer.Deserialize(reader);
}
catch (Exception ex)
{
    // Invalid XML structure - reject invoice
    return false;
}

Step 2: Timbre Fiscal Digital Validation

Ensure the invoice has a valid digital tax stamp:

foreach (ComprobanteComplemento r in factura.Complemento)
{
    for (int y = 0; y < r.Any.Length; y++)
    {
        for (int contador = 0; contador < r.Any[y].Attributes.Count; contador++)
        {
            if (r.Any[y].Attributes[contador].Name == "UUID")
            {
                string uuid = r.Any[y].Attributes["UUID"].Value;
                
                if (string.IsNullOrEmpty(uuid))
                {
                    // No UUID found - reject
                    return false;
                }
                
                // Check for duplicates
                if (!string.IsNullOrEmpty(Exist_UUUID(uuid)))
                {
                    // Duplicate UUID - reject
                    return false;
                }
            }
        }
    }
}

Step 3: Tax Calculation Verification

Validate that tax calculations are correct:

// Verify tax totals match individual tax items
if (factura.Impuestos != null)
{
    decimal totalTraslados = 0;
    
    if (factura.Impuestos.Traslados != null)
    {
        foreach (ComprobanteImpuestosTraslado im in factura.Impuestos.Traslados)
        {
            totalTraslados += im.Importe;
        }
    }
    
    // Verify total matches
    if (Math.Abs(totalTraslados - factura.Impuestos.TotalImpuestosTrasladados) > 0.01m)
    {
        // Tax calculation mismatch - flag for review
        logWarning("Tax calculation discrepancy detected");
    }
}

Step 4: Amount Verification

Ensure the total equals subtotal plus taxes:

// Calculate expected total
decimal expectedTotal = factura.SubTotal 
    - (factura.DescuentoSpecified ? factura.Descuento : 0)
    + (factura.Impuestos?.TotalImpuestosTrasladados ?? 0)
    - (factura.Impuestos?.TotalImpuestosRetenidos ?? 0);

// Verify against declared total (allow 1 cent tolerance for rounding)
if (Math.Abs(expectedTotal - factura.Total) > 0.01m)
{
    // Total calculation error - reject
    return false;
}

Tax Compliance Checks

Supported Tax Types

SMAF validates the following tax types:

IVA (Impuesto al Valor Agregado) - VAT

Tax code: 002
Standard rate: 16%
Border rate: 8%
Exempt: 0%

ISR (Impuesto Sobre la Renta) - Income Tax

Tax code: 001
Applied as withholding (retención)
Variable rates depending on service type

IEPS (Impuesto Especial sobre Producción y Servicios)

Tax code: 003
Special excise tax on specific goods and services
Rates vary by product category

Tax Code Mapping

The system supports both legacy and current SAT tax codes:

switch (im.Impuesto.ToString())
{
    case "IVA":   // Legacy code
    case "002":   // Current SAT code
        poXml.IVA = Convert_Decimales(im.Importe.ToString());
        break;
        
    case "ISR":   // Legacy code
    case "001":   // Current SAT code
        poXml.ISR = Convert_Decimales(im.Importe.ToString());
        break;
        
    case "IEPS":  // Legacy code
    case "003":   // Current SAT code
        poXml.IEPS = Convert_Decimales(im.Importe.ToString());
        break;
}

Validation Status Tracking

Invoices are assigned status codes throughout the validation process:

Status	Description
0	Deleted/Cancelled
1	Active - Pending Review
5	Validated - Approved
7	Validated - In Process

public static string Exist_UUUID(string psUUID)
{
    // Only check active and validated invoices
    string Query = "SELECT CLV_DOC FROM crip_comision_comprobacion ";
    Query += " WHERE CLV_DOC= '" + psUUID + "' AND ESTATUS IN ('1','5','7')";
    // ...
}

Error Handling

Common Validation Errors

public enum ValidationError
{
    InvalidXMLFormat,
    MissingTimbreFiscal,
    DuplicateUUID,
    InvalidRFC,
    TaxCalculationError,
    AmountMismatch,
    UnsupportedVersion
}

public class ValidationResult
{
    public bool IsValid { get; set; }
    public ValidationError? Error { get; set; }
    public string ErrorMessage { get; set; }
    public string UUID { get; set; }
}

Validation Response Examples

Successful Validation:

{
  "isValid": true,
  "uuid": "12345678-1234-1234-1234-123456789012",
  "message": "Invoice validated successfully"
}

Duplicate UUID Error:

{
  "isValid": false,
  "error": "DuplicateUUID",
  "message": "UUID 12345678-1234-1234-1234-123456789012 already exists in the system",
  "existingDocument": "COMP-2026-001234"
}

All UUID validations are case-insensitive to prevent duplicate entries with different casing.

Invoices with validation errors are automatically flagged for manual review by the validation team. They cannot be processed for payment until errors are resolved.

Audit Trail

All validation attempts are logged for audit purposes:

public static void LogValidation(
    string uuid, 
    string usuario, 
    bool isValid, 
    string errorMessage = "")
{
    string Query = "INSERT INTO crip_validation_log (";
    Query += " UUID, USUARIO, FECHA, IS_VALID, ERROR_MESSAGE";
    Query += ") VALUES (";
    Query += " '" + uuid + "',";
    Query += " '" + usuario + "',";
    Query += " NOW(),";
    Query += " " + (isValid ? "1" : "0") + ",";
    Query += " '" + errorMessage + "'";
    Query += ")";
    // Execute query...
}

Best Practices

Early Validation: Validate UUIDs immediately upon file upload before processing other data
Cross-System Checks: Always check both expense reports and direct payment systems for duplicates
Tax Code Support: Support both legacy text codes and current numeric SAT codes
Tolerance for Rounding: Allow 1-cent tolerance in amount calculations due to rounding differences
Audit Logging: Log all validation attempts with timestamps and user information
Error Messages: Provide clear, actionable error messages to users

CFDI XML Processing - XML parsing and data extraction
Email Notifications - Validation status notifications
Database Schema - Validation data storage

Architecture

Business Logic Layer

Data Access Layer

Entities

Integration

SAT Validation

Overview

UUID Validation

UUID Structure

Duplicate Detection for Expense Reports

Duplicate Detection for Direct Payments

Validation Flow

RFC Validation

RFC Format Rules

RFC Extraction

RFC Storage in Database

Invoice Verification Process

Step 1: XML Structure Validation

Step 2: Timbre Fiscal Digital Validation

Step 3: Tax Calculation Verification

Step 4: Amount Verification

Tax Compliance Checks

Supported Tax Types

Tax Code Mapping

Validation Status Tracking

Error Handling

Common Validation Errors

Validation Response Examples

Audit Trail

Best Practices

Build docs developers (and LLMs) love

Architecture

Business Logic Layer

Data Access Layer

Entities

Integration

​Overview

​UUID Validation

​UUID Structure

​Duplicate Detection for Expense Reports

​Duplicate Detection for Direct Payments

​Validation Flow

​RFC Validation

​RFC Format Rules

​RFC Extraction

​RFC Storage in Database

​Invoice Verification Process

​Step 1: XML Structure Validation

​Step 2: Timbre Fiscal Digital Validation

​Step 3: Tax Calculation Verification

​Step 4: Amount Verification

​Tax Compliance Checks

​Supported Tax Types

​Tax Code Mapping

​Validation Status Tracking

​Error Handling

​Common Validation Errors

​Validation Response Examples

​Audit Trail

​Best Practices

​Related Documentation

Build docs developers (and LLMs) love

Overview

UUID Validation

UUID Structure

Duplicate Detection for Expense Reports

Duplicate Detection for Direct Payments

Validation Flow

RFC Validation

RFC Format Rules

RFC Extraction

RFC Storage in Database

Invoice Verification Process

Step 1: XML Structure Validation

Step 2: Timbre Fiscal Digital Validation

Step 3: Tax Calculation Verification

Step 4: Amount Verification

Tax Compliance Checks

Supported Tax Types

Tax Code Mapping

Validation Status Tracking

Error Handling

Common Validation Errors

Validation Response Examples

Audit Trail

Best Practices

Related Documentation