Introduction
Automating the issuance and submission of invoices in Facturae XML format to the SII with AI agents can save time and reduce errors, but you must verify technical prerequisites and tax obligations before going live. This guide explains the technical and regulatory components you need, an operational step‑by‑step flow, GDPR and security controls, and the tests required to move to production.
Reference date for legal and technical checks: 09/09/2026. Before implementing, always confirm the XSD/WSDL, authentication methods and official listings on the AEAT and the Facturae portal (links under Official resources at the end).
Overview: what each system is and why they differ
Facturae (format and versions)
Facturae is Spain’s official XML format for electronic invoicing, intended among other uses for exchange with public administrations and systems that require a standardised XML. The official portal publishes the XSD schemas and technical documentation needed to validate files.
- Facturae portal (schemas and documentation): https://www.facturae.gob.es/
- Practical note: before generating Facturae in production, download and validate against the official XSD for the version in force from the Facturae portal above.
SII (what it sends, purpose and scope)
The Suministro Inmediato de Información (SII) is a system managed by the Agencia Estatal de Administración Tributaria (AEAT) for receiving invoicing records (issued and received invoice data) to improve VAT control and traceability. The AEAT maintains a technical section with service manuals for submitting data.
- SII documentation and manuals (AEAT): https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html
- Note: obligation and scope of SII vary according to AEAT resolutions and criteria; not all companies are required to participate. Check the official list and associated resolutions on the AEAT electronic office before making decisions.
FACe and VERI*FACTU: operational roles and differences
- FACe is the Central Entry Point for invoices directed at Public Administration bodies; its purpose is to receive invoices intended for public organisations (FACe portal: https://proveedores.face.gob.es/).
- VERIFACTU (VERiFACTU / VeriFactu) is the AEAT technical framework oriented to verifiable invoicing and to Billing Information Systems (SIF); it defines technical and functional requirements that may apply depending on use and volume (AEAT — VERI*FACTU): https://sede.agenciatributaria.gob.es/Sede/iva/sistemas-informaticos-facturacion-verifactu.html
None of these services is identical to the SII: FACe handles invoice reception for public bodies; SII handles VAT reporting to the AEAT. VERI*FACTU provides verification mechanisms and technical requirements with scope and conditions set out in the linked official documentation.
Who is obliged and what voluntary options exist?
Whether an entity is required to use SII depends on specific provisions published by the AEAT (resolutions, orders and criteria). Do not generalise: consult the official list and published resolutions.
How to check if your company is obliged (practical steps)
- Visit the SII section on the AEAT electronic office and review the available information and regulations: https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html
- Check the regulation or resolution that details obliged subjects and rollout dates (consult resolutions and orders in the BOE: https://www.boe.es/).
- If in doubt, consult your tax adviser or AEAT support channels (contact details on the AEAT electronic office).
- Keep a screenshot or reference (date and URL) of the document consulted as part of your compliance records.
Mandatory technical checks before integrating (verify with AEAT)
These are the key technical pieces you must confirm in the official manuals before developing or procuring a solution.
Facturae schemas and XML validation
- Validate XML against the official XSD for the Facturae version indicated on the portal. Common critical fields: issuer/recipient identifiers (NIF), taxable bases, VAT rates, bases and totals, invoice series and number, issue date and operation codes.
- Include XSD validation in your local pre‑send pipeline and reject invoices that fail validation. Download schemas and documentation from: https://www.facturae.gob.es/
Authentication and access methods for AEAT services
The AEAT publishes connection details (WSDL/web services) and procedures for access and authentication. Specific requirements (certificates, service identifiers, WSDL, endpoints) appear in the SII technical documentation and the service description PDFs:
- SII (AEAT): https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html
- SII web service description (technical PDF): https://sede.agenciatributaria.gob.es/staticfiles/Sede/Procedimientoayuda/G417/FicherosSuministros/V11/SII-Descripcion-ServicioWeb-v1-1eses.pdf
Avoid assuming OAuth or other undocumented methods: rely on the official guide and the WSDL/PDFs published by the AEAT for access and credential acquisition.
Signing, sealing and integrity requirements
Some flows (and especially specific SIF/VERIFACTU models) may impose additional integrity, sealing or registration requirements. Whether you must sign the XML or whether channel authentication suffices depends on the service and schema version; consult AEAT technical documentation and VERIFACTU requirements:
- AEAT — SII: https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html
- AEAT — VERI*FACTU: https://sede.agenciatributaria.gob.es/Sede/iva/sistemas-informaticos-facturacion-verifactu.html
Do not assume a signing requirement without confirming it in the official documents: check the service PDF and the VERI*FACTU sections.
Limits, submission rates, timings and retry policies
The AEAT publishes service specifications (WSDL and PDFs). Before designing your system, consult the technical section for limits, maximum payload sizes and retry or rate limit policies:
- AEAT — SII technical documentation: https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html
- SII service technical description (traffic and error details): https://sede.agenciatributaria.gob.es/staticfiles/Sede/Procedimientoayuda/G417/FicherosSuministros/V11/SII-Descripcion-ServicioWeb-v1-1eses.pdf
If the technical manual does not specify an absolute limit, or publishes it elsewhere, design your architecture with queues and exponential backoff to avoid rejections and ask AEAT support for clarifications if needed.
Proposed architecture and step‑by‑step flow using AI agents
Below is a modular, non‑prescriptive flow we use as a baseline in the Momentum Process (audit, architecture, local deployment, integration and optimisation).
Step 0 — design and pre‑requirements (data policy and scope)
Minimum checklist before starting:
- Define which invoice series and types you will automate (e.g. invoices to private customers vs invoices to the Administration).
- Review cloud provider contracts and whether an HSM is required for key protection.
- Retention policy and audit trail (logs of submissions, responses and retries).
- Assess whether a DPIA is required (see GDPR section).
Step 1 — extraction and enrichment with AI agents
What an AI agent can do:
- OCR and data extraction from received invoices.
- Classification of line items and mapping to accounting accounts.
- Pre‑fill required Facturae fields (always with subsequent validation).
Recommended controls:
- Validate extracted data with rules (for example: NIF pattern checks) and perform human sampling during the pilot.
- Record the agent’s decision in the audit trail (proposed value, confidence and who or what confirmed it).
Momentum experience — how we work in practice:
At Momentum Logic AI we deploy in phases: first a sandbox pilot with integration tests and XSD validation, then a controlled production period with sampling and human checks agreed with the client, and finally full automation once accepted. During the pilot we run submission tests and review AEAT responses, documenting evidence (test files, logs and sampling decisions). These steps are part of our Momentum Process (technical audit, deployment and optimisation).
Note: pilot scope (duration, sample size) is agreed with each client according to risk and volume.
Illustrative example (hypothetical): a self‑employed sole trader (autónomo) issuing 30 invoices/month could automate extraction and pre‑fill in minutes; with automated validations you reduce manual rejection handling. (Hypothetical example; adjust percentages to your case.)
If you would like help assessing your specific situation and what to automate first, we can review your use case and advise on a pragmatic pilot.
Step 2 — Facturae XML generation and local validation
- Map ERP fields to the mandatory XSD elements.
- Run XSD and business‑rule validations (NIF, VAT codes, arithmetic sums, series). Log and correct errors before signing or sending.
Step 3 — signing/sealing and preparation for submission
Technical options:
- Electronic signature with a qualified certificate or use of an HSM to protect keys.
- Inclusion of a timestamp seal if required by the operation.
Note: confirm in AEAT documentation whether delivery to SII requires signing the XML or whether channel authentication suffices: https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html. For VERI*FACTU‑specific requirements consult: https://sede.agenciatributaria.gob.es/Sede/iva/sistemas-informaticos-facturacion-verifactu.html
If you prefer us to set this up with you, Momentum covers this phase during architecture and deployment.
Step 4 — submission to SII / VERI*FACTU (or FACe when applicable) and handling responses
Selection criteria:
- Submit to SII when you are obliged to, or decide to supply VAT records.
- Submit to FACe only when an invoice must be delivered to a public body as a supplier (FACe: https://proveedores.face.gob.es/).
Operational flow:
- Call the service (WSDL/web service) and persist the request with a unique correlation ID.
- Process responses: accepted, pending, rejected. Implement retries with backoff and keep logs for accounting reconciliation.
- Store the full trace (request, response, retry logs) for audit purposes.
Practical integration: link this flow with your ERP/accounting system to flag states and reconcile entries automatically.
You can also consult our guide on automating recurring invoicing and bank reconciliation to see how to connect this with accounting and reconciliation processes: our guide on automating recurring invoicing and bank reconciliation
Testing, approval and go‑live
- Use AEAT homologation/sandbox environments where available. Perform volume, latency and error‑case tests (invalid NIF, validation rejections, timeouts).
- Document tests and keep dated evidence (files, logs, screenshots).
- Define clear production acceptance criteria with your tax and technical teams (for example: percentage of files passing XSD validation, tolerance for retries, and load tests that reflect expected volume). Consult AEAT on formal homologation requirements if applicable: https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html
Security, data protection and compliance (GDPR)
Minimum checklist:
- Carry out a DPIA where you process sensitive personal data or the automation changes the scale of processing.
- Encrypt in‑transit (TLS) and at rest any databases holding invoices.
- Role‑based access control and immutable logging for critical operations.
- DPA/contractual arrangements with cloud providers and clauses on subprocessors when external AI services are used.
- Avoid sending data to third‑party models without contract and technical guarantees. Record automated decisions and the human verification criteria.
Operation, monitoring and operational limits
Recommended metrics:
- AEAT rejection rate (% of submissions rejected).
- Average response latency per submission.
- Mean time to resolution for rejections.
- Retry rate and post‑retry success rate.
Implement dashboards with alerts (for example, when rejection rate breaches an agreed threshold) and escalation procedures.
Common errors and practical fixes
- XSD validations: maintain a unit test suite with valid and invalid examples.
- Misformatted NIF/CIF: validate with regex and the control digit where applicable.
- Tax base mismatches: check arithmetic sums and rounding before sending.
- Rate limit rejections: implement queuing and exponential backoff.
- Authentication errors: verify certificates and expiry dates.
For each error code, consult the SII technical manual for the precise meaning: https://sede.agenciatributaria.gob.es/staticfiles/Sede/Procedimientoayuda/G417/FicherosSuministros/V11/SII-Descripcion-ServicioWeb-v1-1eses.pdf
Practical architecture example (simplified fictional case)
Minimum suggested architecture (example):
- UI/ERP -> AI agent (OCR + classification) -> Facturae validator (XSD + rules) -> Signing/HSM -> SII submission -> Recording and reconciliation.
Responsibility table (hypothetical example):
- ERP: commercial and client data.
- AI agent: extraction and pre‑fill.
- Validator: XSD and business rules.
- Signing/HSM: key management and signing.
- Submission component: calls to AEAT and retry handling.
Pre‑deployment checklist:
- XSD validation against the official version (Facturae portal).
- Credentials for AEAT sandbox access.
- Load tests that represent realistic peaks.
TABLE: PAST / PRESENT / FUTURE (reference 09/09/2026)
| Period | Summary | Source / note |
|---|---|---|
| PAST | Initial SII roll‑out and publication of the first resolutions and orders related to its implementation in the late 2010s; Facturae already existed as the official electronic invoicing format for Administration submissions. | Regulations and orders published in the BOE — consult the BOE for historic orders and resolutions: https://www.boe.es/ |
| PRESENT (09/09/2026) | The AEAT maintains SII technical documentation and offers applications such as VERI*FACTU; there are portals for Facturae and FACe. The exact scope of obliged entities must be checked on the AEAT electronic office. | https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html (consulted 09/09/2026) |
| FUTURE | Announcements and analysis exist on VERI*FACTU evolution and potential changes to schemas or SII scope; any extension or future obligation dates must be confirmed via official AEAT or BOE resolutions. | Check AEAT and BOE news and resolutions for updates (links under Official resources). |
Conclusion and recommended next steps
Integrating Facturae and the SII into an automated flow with AI agents is feasible and brings efficiency, but you must verify schema versions, authentication methods, submission limits and any signing requirements before production. Practical next steps:
- Verify the Facturae XSD and download the current version from: https://www.facturae.gob.es/
- Confirm WSDL/web services and authentication methods in the AEAT SII technical manual: https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html
- Obtain credentials and test in the AEAT sandbox where available.
- Perform a DPIA if required and finalise DPAs with your providers.
- Run volume tests and define acceptance metrics.
If you would like us to evaluate your specific case, request a Free Assessment and we will advise which parts to automate first.
Official resources (consulted / for verification)
- AEAT — Suministro Inmediato de Información (SII): https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html (consulted 09/09/2026)
- Facturae (official portal and schemas): https://www.facturae.gob.es/ (consulted 09/09/2026)
- FACe — Central Entry Point for invoices: https://proveedores.face.gob.es/ (consulted 09/09/2026)
- VERI*FACTU (AEAT): https://sede.agenciatributaria.gob.es/Sede/iva/sistemas-informaticos-facturacion-verifactu.html (consulted 09/09/2026)
- SII service technical description (AEAT PDF): https://sede.agenciatributaria.gob.es/staticfiles/Sede/Procedimientoayuda/G417/FicherosSuministros/V11/SII-Descripcion-ServicioWeb-v1-1eses.pdf
- BOE (search resolutions and orders): https://www.boe.es/
FAQs
- Who is currently obliged to use SII and how do I verify?
- Check the list and resolutions on the AEAT SII electronic office; if unsure, consult your tax adviser.
- Is Facturae the same as SII or can I use FACe to meet SII obligations?
- No. Facturae is the format; FACe is a portal to deliver invoices to the Administration; SII is the supply of VAT records to the AEAT. They are not interchangeable without checking applicable rules.
- What authentication methods does AEAT accept for SII services?
- Exact methods and credential acquisition are documented in the AEAT technical section and service PDFs referenced above: https://sede.agenciatributaria.gob.es/Sede/iva/suministro-inmediato-informacion.html
- What checks should I run before sending automated invoices to SII?
- XSD validation, business rules (NIF, bases, VAT), signing/sealing if applicable, sandbox tests and GDPR compliance.
- How do I ensure GDPR compliance when using AI agents for invoicing?
- Perform a DPIA if required, encrypt data, set DPAs with providers, log automated decisions and keep human checks for sensitive operations.
This article was drafted with the support of artificial intelligence and reviewed by qualified Momentum Logic AI staff before publication.
- Momentum Logic AI Team . momentumlogicai.es . LinkedIn
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