Greece’s mandatory B2B e-Invoicing enters its second phase in October 2026

• Greece introduced mandatory structured e-Invoicing for domestic B2B transactions in phases during 2026. The first phase started on 2 March 2026, while the second phase is scheduled to begin on 1 October 2026 for the remaining Greek-established businesses. [rtcsuite.com], [rtcsuite.com]
• The mandate builds on the existing myDATA digital reporting framework. Invoices must be transmitted through an accredited e-Invoicing service provider or AADE’s free invoicing tools, validated through myDATA and returned with a unique MARK and QR code. [rtcsuite.com], [rtcsuite.com]
• Businesses entering Phase 2 should complete their ERP integration, transaction mapping, provider configuration and end-to-end testing before October. The implementation must cover more than invoice generation and should include submission, validation, MARK retrieval, QR-code processing, error management and archiving. [rtcsuite.com], [rtcsuite.com]

Greece’s transition to mandatory structured B2B e-Invoicing is already underway. The first group of businesses entered the mandatory regime on 2 March 2026, and the next major deadline is approaching. From 1 October 2026, all remaining Greek-established businesses falling within the second phase are expected to enter the mandatory e-Invoicing framework. [rtcsuite.com], [rtcsuite.com]

The Greek model is not a completely new invoicing environment. It builds on the country’s existing myDATA, or My Digital Accounting and Tax Application, framework. Greek businesses have used myDATA for digital reporting and electronic bookkeeping for several years. The 2026 mandate adds a structured invoice-exchange layer to that reporting infrastructure, bringing the issuance, validation and reporting of invoices into a more integrated process. [rtcsuite.com], [rtcsuite.com]

Businesses operating in Greece should therefore not treat the October deadline as a simple extension of existing invoice-data reporting. Mandatory e-Invoicing affects the underlying invoicing process, including how invoices are created, transmitted, validated, delivered to customers and recorded in accounting systems.

Phase 1 has already started

The first mandatory phase applies to larger resident businesses and began on 2 March 2026. This date replaced an earlier planned start of 2 February 2026. A controlled transition period followed the March start date to support the onboarding of the first group of businesses. [rtcsuite.com], [rtcsuite.com]

According to RTC, the first phase targets Greek-resident businesses meeting the relevant turnover threshold, including domestic B2B supplies of goods and services. The scope also extends to certain supplies to customers outside the European Union. For B2B transactions with customers in other EU Member States, structured e-Invoicing remains subject to a different treatment, and businesses must be able to support an alternative compliant invoice format where the customer does not accept the structured invoice. [rtcsuite.com], [rtcsuite.com]

Businesses included in Phase 1 should now be operating their mandatory solution. Their experience also provides an important indication of the operational issues that Phase 2 businesses may encounter, including data-quality problems, mapping errors, rejected invoice submissions, delays in receiving validation responses and difficulties reconciling the e-Invoice status with the underlying ERP document.

Phase 2 begins on 1 October 2026

The second phase is scheduled to begin on 1 October 2026 and will bring the remaining Greek-established businesses into the mandatory B2B e-Invoicing regime. RTC indicates that this phase is accompanied by a transition period extending through the end of 2026. However, businesses should not interpret the transition period as a reason to postpone preparation until October. [rtcsuite.com], [rtcsuite.com]

A compliant solution must be operational before invoices within scope are issued. Businesses should therefore use the remaining preparation period to complete system changes, connect to the selected transmission channel and test the full invoice lifecycle.

This is especially important for multinational groups that issue Greek invoices from a central or regional ERP environment. The Greek legal entity may be part of a global billing model, shared service centre or centralised accounts-receivable process. The group must ensure that local Greek requirements are integrated into that model without disrupting global order-to-cash processes.

How the Greek e-Invoicing model works

Greece operates a controlled e-Invoicing model built around the AADE myDATA platform. Structured invoices are transmitted electronically through approved channels and validated as part of the myDATA process. Businesses may generally use an accredited e-Invoicing service provider or the free invoicing applications made available by AADE. [rtcsuite.com], [rtcsuite.com]

Following successful transmission, the invoice receives a unique registration identifier known as the MARK. A QR code is also associated with the validated document. These elements enable the invoice to be connected to the information recorded in myDATA and support verification of the document. [rtcsuite.com], [rtcsuite.com]

For businesses with significant transaction volumes, direct manual invoicing through a government application is unlikely to be a sustainable solution. Integration between the ERP system and an accredited provider will normally be required to automate the creation, transmission and processing of invoice data.

The solution must also return relevant information to the ERP. It is not sufficient to send an invoice file out of the accounting system. The business should capture the validation result, MARK, QR code and document status, and associate them with the corresponding accounting and customer records. Failed or rejected invoices must enter a controlled exception-management process.

Key readiness areas for Phase 2 businesses

The first priority is determining the scope of transactions and legal entities affected. Businesses should identify domestic B2B transactions, relevant exports and any transaction flows subject to different rules. Particular attention should be given to credit notes, debit notes, advance payments, self-billing, cancellations, corrective invoices and intercompany transactions.

Master data must also be reviewed. Customer tax numbers, addresses, legal names, invoice classifications, product information, tax codes and payment details must be sufficiently complete and accurate to support structured e-Invoicing. Data that may have been acceptable on a visually readable PDF can cause an electronic invoice to fail automated validation.

ERP tax codes and invoice types should be mapped to the required myDATA classifications and document categories. This mapping should cover standard sales as well as less frequent transactions. Businesses should avoid focusing testing only on straightforward domestic sales invoices.

The integration should support the complete process from invoice creation to successful delivery and accounting reconciliation. This includes structured invoice generation, submission to the provider or AADE tool, myDATA transmission, validation, MARK retrieval, QR-code creation, customer delivery, status reporting and compliant storage. [rtcsuite.com], [rtcsuite.com]

Testing should include negative scenarios. Businesses should verify what happens when customer data are incomplete, connectivity fails, myDATA rejects a document, the provider is unavailable or an invoice must be corrected after submission. Clear ownership is required across tax, finance, accounts receivable, IT, customer service and the external service provider.

Broader digital compliance environment

Mandatory B2B e-Invoicing is only one part of Greece’s digital tax environment. Businesses may also be subject to myDATA reporting, B2G e-Invoicing and digital delivery-note requirements for the movement of goods. Each layer has its own technical and operational requirements. [rtcsuite.com], [rtcsuite.com]

Companies should therefore avoid implementing the October mandate as an isolated technical project. Invoice data, goods-movement data, accounting entries and VAT reporting should remain consistent. Differences between these data sets may create reconciliation problems and increase the risk of queries from the Greek tax authorities.

What businesses should do now

Businesses entering Phase 2 should confirm their implementation scope and transmission model immediately. They should appoint clear owners, complete the design of the ERP integration and begin testing with representative transaction scenarios.

They should also verify that their solution supports MARK retrieval, QR-code generation, structured invoice delivery and automated error handling. Internal procedures must explain when an invoice is considered successfully issued, how rejected documents are corrected and how discrepancies between the ERP, the service provider and myDATA are resolved.

The move to mandatory e-Invoicing is not merely a change in invoice format. It introduces a controlled digital process in which invoice issuance and tax reporting become closely connected. Businesses that wait until October to test this process risk rejected invoices, customer disputes, delayed collections and inconsistencies in their myDATA records.

The next phase begins on 1 October 2026. Businesses within scope should use the remaining time to move from design to testing and from testing to production readiness.

Further information is available in RTC’s overview of Greece’s 2026 e-Invoicing dates and requirements. [rtcsuite.com]