Greece E-Invoicing 2026: What ERP Vendors Need to Know

Greece's B2B e-invoicing mandate went live on March 2, 2026. Large enterprises — those with gross revenues above €1 million in the 2023 tax year — are now required to issue and transmit structured electronic invoices through the AADE myDATA platform. A two-month adjustment window runs until May 3, with broader SME coverage following in October.

If your ERP platform serves customers operating in Greece, this is not a future-state problem. The integration requirement is active now.

Timeline: Key Dates at a Glance

Date	Obligation
March 2, 2026	Mandatory e-invoicing via myDATA for large enterprises (>€1M revenue in 2023)
May 3, 2026	End of adjustment period — both legacy and myDATA systems allowed in parallel until this date
October 1, 2026	Mandatory e-invoicing for all remaining VAT-registered businesses (Phase 2)
December 31, 2026	End of Phase 2 adjustment period

The adjustment period is not a grace period in the Belgian sense. Greek tax authority AADE expects large enterprises to be progressively migrating to myDATA between March 2 and May 3 — not simply delaying. Parallel operation (legacy systems alongside myDATA) is permitted during this window, but businesses are expected to demonstrate active migration efforts.

How myDATA Works: The Clearance Model

Greece operates a Continuous Transaction Controls (CTC) clearance model. Unlike Peppol-based systems where invoices are exchanged directly between trading partners via a network, Greek B2B invoices must be submitted to the AADE myDATA platform and receive a Unique Invoice Identifier (UID) before they are considered legally valid.

The process is:

Your ERP generates the invoice in EN 16931-compliant XML
The invoice is submitted to myDATA via REST API
AADE validates the invoice and returns a UID
The UID is embedded in the invoice before delivery to the buyer
The buyer's system can verify the UID against myDATA to confirm authenticity

This is a fundamental architectural difference from Peppol-first markets like Belgium or the Netherlands. The myDATA clearance step is not optional post-delivery metadata — it is a prerequisite to the invoice being legally valid. ERP integrations must handle the submission-and-UID-retrieval cycle before the invoice is sent to the buyer.

Technical Requirements

Invoice Format

myDATA accepts EN 16931-compliant XML. Greece does not have a proprietary format equivalent to Poland's FA(3) or Italy's FatturaPA — the European standard is the baseline. In practice, this means:

UBL 2.1 and UN/CEFACT CII (Cross Industry Invoice) are both accepted
The XML must be valid against the EN 16931-1 semantic data model and EN 16931-3 binding rules
AADE publishes its own myDATA XML schema alongside the EN 16931 alignment documentation

Key required fields include: Greek VAT number (AFM) of both issuer and recipient, invoice type codes, line-level VAT breakdown, and the AADE classification codes for income and VAT categories. The classification codes are specific to myDATA and have no EN 16931 equivalent — they are an AADE extension that must be mapped correctly.

Submission API

myDATA uses a REST API with JSON payloads. Note: while the invoice document itself is XML, the API transport layer is JSON. Your integration must:

Wrap the XML invoice in the myDATA JSON envelope
Authenticate using the AADE-issued User ID and Secret Key (obtained per taxpayer from the myDATA portal)
Handle both synchronous responses (successful UID return) and error responses (validation failures with structured error codes)

The API has two modes:

Standard submission — single invoice submitted synchronously. AADE returns the UID in the response. Appropriate for low-volume workflows or real-time invoice generation.

Batch submission — multiple invoices submitted in a single request. AADE processes asynchronously and returns a batch identifier. The ERP must poll for results. Appropriate for high-volume environments or period-end bulk submission.

Authentication is per-company, not per-session. The User ID and Secret Key are stable credentials assigned to each Greek taxpayer. For ERP vendors serving multiple Greek customers, this means managing per-customer credential sets — a credential management pattern, not a shared authentication layer.

Submission Deadlines

Greece does not require real-time clearance at the moment of invoice issuance (unlike Italy's SDI model). The submission timing requirements are:

Monthly VAT filers: invoices must be submitted to myDATA by the 20th of the following month
Quarterly VAT filers: invoices must be submitted by the 20th of the month following the quarter end

This gives ERP vendors some flexibility on submission timing, but it creates a compliance monitoring problem: your system must track which invoices have been submitted and confirm UIDs received, with an audit trail that connects each invoice to its myDATA submission record.

Who Is Affected

Phase 1 (active from March 2, 2026):

Greek-resident businesses with gross revenues exceeding €1 million in the 2023 fiscal year
Scope: domestic B2B transactions and exports outside the EU
Intra-EU B2B transactions are currently out of scope (subject to ViDA from 2030)

Phase 2 (active from October 1, 2026):

All remaining VAT-registered businesses in Greece
The same scope applies: domestic B2B and non-EU exports

Out of scope:

B2C transactions
Intra-EU supplies of goods and services
Businesses with no Greek VAT registration

Foreign businesses invoicing Greek customers for VAT-taxable supplies within Greece may be in scope depending on their VAT registration status in Greece. If your ERP serves customers with Greek VAT registrations, assume the mandate applies and confirm the specific scope with local tax advisors.

Penalties

Non-compliance carries financial consequences that are proportional to the transaction value:

Transaction Type	Penalty
VATable B2B transactions	50% of the VAT amount on the non-compliant invoice
Non-VAT transactions	€500 (simplified accounting systems) or €1,000 (double-entry systems) per infraction

There is also a structural penalty that is harder to quantify: invoices not cleared through myDATA do not receive a UID. Buyers attempting to claim input VAT deduction on UID-less invoices face significant audit risk and may be denied the deduction. In practice, large Greek buyers are already refusing to accept invoices without a valid myDATA UID — regardless of the formal penalty timeline.

Additionally, non-compliant businesses risk exclusion from public tenders and government contracts.

What ERP Vendors Should Do

Map the myDATA classification codes

The most common implementation failure is treating myDATA as a straight EN 16931 submission. It is not. The AADE classification codes — which categorise income type and VAT treatment per the Greek VAT code — are mandatory extensions that must be added to every invoice line. There is no automatic mapping from standard VAT rate fields to Greek classification codes. This is a data model problem that must be solved before any API integration work begins.

Implement credential management for Greek entities

Unlike Peppol, where your platform can use a single access point for all customers, myDATA authentication is per-taxpayer. Each Greek customer has their own AADE User ID and Secret Key. Design your integration to store and manage these credentials per entity, not per platform.

Handle the UID storage requirement

The myDATA UID is the legally required proof that an invoice has been cleared. Your platform must store the UID associated with each submitted invoice and make it retrievable for audit purposes. It also needs to appear on the invoice document delivered to the buyer. Plan your data model accordingly before building the submission flow.

Test in the myDATA sandbox

AADE operates a sandbox environment that mirrors the production API. It is the only way to validate your XML format, classification code mapping, and submission flow before going live with real transactions. Greek tax advisors and myDATA documentation specify exact test credentials and endpoints.

Build submission tracking and retry logic

Batch submissions return async results. Network failures happen. Your integration needs a queue-and-retry mechanism that tracks submission status per invoice and can resubmit on failure without creating duplicate submissions. The myDATA API provides idempotency mechanisms — use them.

FAQ

Does myDATA replace Peppol for Greece?

Yes, for domestic B2B. Greece has not mandated Peppol as its e-invoicing network — myDATA is the national clearance platform. Peppol remains relevant for cross-border EU transactions and may become more relevant once ViDA's cross-border reporting rules take effect from 2030, but for domestic Greek B2B today, myDATA is the only compliant path.

Can invoices be submitted in PDF or via email?

No. PDF invoices do not meet the mandate requirements. The invoice must be submitted as structured XML to myDATA to receive a UID. Without the UID, the invoice is not legally valid for Greek B2B purposes.

What happens to invoices issued before the mandate that haven't been cleared?

Historical invoices issued before March 2, 2026 are not retroactively required to be submitted through myDATA. The obligation applies to invoices issued on or after the mandate date. However, if you are in the adjustment period (through May 3), invoices issued via legacy systems during that window should be migrated to myDATA submission as quickly as practically possible.

Does the mandate apply to foreign companies invoicing Greek customers?

It depends on VAT registration status. Foreign businesses with a Greek VAT registration and domestic VAT liability may be in scope. Foreign businesses invoicing Greek customers under reverse-charge arrangements for cross-border services are generally out of scope. Confirm the specific position with a Greek tax advisor — the rules depend on the nature of the supply and the registration status of both parties.

What is the submission deadline for a September invoice?

For monthly VAT filers, a September invoice must be submitted to myDATA by October 20. For quarterly filers, it would need to be submitted by October 20 (end of Q3). The 20-days-after-month-end rule applies to the period in which the invoice appears in the VAT ledger, not necessarily the invoice date.

Can my platform use a single myDATA API connection for all Greek customers?

No. Authentication is per-taxpayer. Each Greek customer must provide their own AADE User ID and Secret Key, which your platform uses to submit invoices on their behalf. There is no shared or delegated access model equivalent to a Peppol access point managing multiple customers under one set of credentials.