Which identifiers should be stored for an e-invoice?

Detailed explanation

When it comes to identifiers in e-invoices, a distinction must be made between what is actually required and what is merely good technical practice. Section 74 of Act No. 222/2004 Coll. on VAT prescribes the content of an invoice: serial number, date of issue and delivery, identification of the seller and buyer (name, address, VAT registration number), and other commercial details. The technical standard EN 16931 and Peppol BIS Billing 3.0 (to which Section 76a of the VAT Act refers as the ‘technical standard for electronic invoicing’) add mandatory structured fields to this — the invoice number, identifiers for both the seller and the buyer, and the Peppol EndpointID, via which the document is routed within the network to a specific provider. In addition, each company or software system may also store its own technical identifiers (internal invoiceId, XML hash, provider’s submissionId, statusId/eventId, idempotency key) — these facilitate the matching of webhooks, distinguishing retries from duplicates, and handling support queries, though no law or standard specifically requires them.

What is actually required by law and the standard

Section 74 of the VAT Act lists the mandatory content of an invoice, including the identification of the parties and the serial number. Section 76a of the VAT Act (inserted by Act No. 385/2025 Coll., effective from 1 January 2027) does not itself contain any specific list of technical identifiers — it imposes general obligations on the delivery-service provider (to verify formal requirements, reliably identify the sender and recipient, and prove the date and time of dispatch/delivery/receipt) and refers to the EN 16931/Peppol BIS standard for technical details. Internal technical identifiers (hash, submissionId, idempotency key) are not part of either the Act or this standard — they are recommendations for building reliable software.

Practical examples

• The invoice contains the company registration number and VAT number of both parties, as required by law, and a serial number — this must be correct, otherwise the invoice is invalid.
• In addition, the company keeps an internal record of the invoiceId and XML hash so that it can prove exactly which file was sent — this helps in the event of a complaint, but is not required by law.
• The webhook from the provider carries its own submissionId and statusId — the company stores these for support purposes, not because the law requires it.

Most common mistakes

• “The law requires the XML hash and idempotency key to be stored.” It does not — these are recommendations based on technical best practice, not a legal obligation.
• “The invoice number is sufficient.” By law, the identification of the parties, including company registration number/VAT number and dates, is also required; for integration purposes, however, more information is useful.
• “The Peppol EndpointID is merely a technical matter with no connection to the law.” It is part of a standard to which the law (Section 76a) directly refers, so it is relevant.

Conclusion

Section 74 and the applicable e-invoicing rules distinguish required invoice and party identifiers, including the EndpointID, from additional technical identifiers retained as good integration and audit practice.

Legal basis

• Act No. 222/2004 Coll. on VAT, Section 74 (invoice requirements)
• Act No. 222/2004 Coll. on VAT, Section 76a (as amended by Act No. 385/2025 Coll.) — general obligations of the delivery-service provider, reference to the technical standard
• EN 16931 and Peppol BIS Billing 3.0 — mandatory document and party identifiers, EndpointID

Related questions

• What is an EndpointID?
• How should I archive the evidence?

This is not legal advice. Sources: Act No. 222/2004 Coll. on VAT (Section 74, Section 76a as amended by Act No. 385/2025 Coll.), official methodological and information materials from the Slovak Financial Administration on e-invoicing (which do not address this specific topic of technical identifiers), OpenPeppol BIS Billing 3.0 and EN 16931. Verified on 8 July 2026.