SIFEN API: electronic invoicing integration over REST

It is a REST e-invoicing gateway for Paraguay, built for systems that are not Odoo: an in-house or third-party ERP, a point of sale, an e-commerce site, recurring billing. You build the document as JSON. The gateway builds the XML, validates it, signs it with your certificate, sends it to SIFEN, polls the batch and stores the XML and the KuDE.

The model is asynchronous: every issue answers 202 with an identifier, and the result is polled or arrives by webhook. There is no synchronous mode. Average latency is under 2 seconds, so polling the result every second feels almost immediate without holding a connection open.

If you already use Odoo you probably do not need the API: the Odoo module uses this same gateway.

With a POST /v1/sifen/documents. The body has four parts: document_kind (factura, autofactura, nota_credito, nota_debito or remision), invoice_data (the document: receiver, items, payment condition), params_data (the issuer and the timbrado) and context (certificate, CSC, environment and a reference of your own).

curl -X POST https://sifen.ecav.com.py/v1/sifen/documents \
  -H "Authorization: Bearer sk_test_XXXXXXXXXXXXXXXX" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: FAC-2026-0001" \
  -d @factura.json

{
  "document_kind": "factura",
  "invoice_data": {
    "establecimiento": "001",
    "punto": "001",
    "tipoTransaccion": 2,
    "tipoImpuesto": 1,
    "moneda": "PYG",
    "condicion": { "tipo": 1, "entregas": [{ "tipo": 1, "monto": 110000 }] },
    "cliente": { "ruc": "5012345-6", "razonSocial": "Cliente SA" },
    "items": [{ "descripcion": "Servicio mensual", "cantidad": 1, "precioUnitario": 110000 }]
  },
  "params_data": { "ruc": "80000000-7", "timbradoNumero": "12345678" },
  "context": {
    "certificate_b64": "<.p12 en base64>",
    "certificate_password": "<contraseña del .p12>",
    "csc": "<CSC>",
    "csc_id": "0001",
    "environment": "test",
    "document_ref": "FAC-2026-0001"
  }
}

The gateway answers right away, without waiting for the DNIT:

HTTP/1.1 202 Accepted

{
  "request_id": "req-8f3a1c2e9b7d4e60",
  "poll_url": "/v1/sifen/documents/req-8f3a1c2e9b7d4e60",
  "webhook_will_fire": true,
  "processing_delayed": false
}

Two details that save trouble:

• Idempotency-Key. If you retry after a timeout with the same key you get the same request_id and the document is not issued twice. The key is unique per tenant. Use, for example, the document's identifier in your system.
• Certificate. It goes in context as certificate_b64 and certificate_password. The other ways to deliver it are in the integration manual.

The complete field reference by document type, the webhook verification code and the certificate options are not published here: they are delivered in the integration manual when your account is activated. Ask for your key and we will send it.

Every state change can be delivered with a POST to your URL. Deliveries are signed with HMAC-SHA256 using your webhook secret, and carry headers to verify the signature, identify the event and drop repeats. Delivery is at least once, so one may repeat; if your endpoint fails many times in a row, the gateway disables it. Webhooks and polling coexist: you can use both. The verification code is in the integration manual.

A document the DNIT rejects does not use up quota: it is deducted only when SIFEN accepts the document.

The plans are those of ECAV SIFEN, by monthly document volume, and apply to all three routes (API, Odoo and portal). There is more detail on pricing.

Fair use on Business: above 3,000 documents a month we reach out to make sure you are on the best plan.