Greece B2B E-Invoicing Phase 2: An October 2026 Checklist

If your business sat out the first half of 2026 because Greece's e-invoicing mandate only reached the big companies, October 1 is your date. Phase 2 pulls every remaining business established in Greece into mandatory structured B2B e-invoicing, and the transition window behind it closes on December 31, 2026. Here is what changes, what is already in force, and what to do before and during the month.

What Phase 2 actually changes

Greece made structured electronic invoicing the legal standard for domestic B2B transactions under Law 5222/2025, published in July 2025, which amends Article 14 of Law 4308/2014, the Greek Accounting Standards law. The rollout is phased by size. Businesses with gross revenues over €1 million in the 2023 tax year began mandatory compliance on March 2, 2026. Phase 2 covers all remaining taxpayers established in Greece, starting October 1, 2026, with a transition period running through December 31, 2026.

Two things change in practice. First, paper and PDF invoices no longer meet the requirement for domestic B2B sales: invoices must be structured electronic documents conforming to the EN 16931 standard. Second, every invoice must be transmitted to AADE's myDATA platform for validation.

The legal route here runs through the EU. Council Directive (EU) 2025/516, adopted on March 11, 2025 as part of the VAT in the Digital Age package, gave member states the option to introduce mandatory e-invoicing for domestic B2B transactions, and the Greek tax authorities planned to implement it.

The mandate also sits inside a wider digitization program. Under the Greece 2.0 plan, business modernization includes a $467 million investment in SME digitalization, alongside digital tax authority tools and mandatory electronic invoicing.

The myDATA layer that already applies to you

None of this arrives on an empty shelf. myDATA has been live for years, and some of what it demands already binds you.

Electronic reporting through myDATA is a mandatory obligation in Greece under Law 4646/2019, covering all sales invoices in real time along with revenue and expense classifications. Entities subject to Greek Accounting Standards transmit their e-book data to the Independent Authority for Public Revenue (AADE) through the myDATA REST API.

Sales to the government are already covered too. Law 4972/2022, published in September 2022, mandates the electronic invoice for all sales made to the government regardless of transaction value, and adds sanctions for failing to transmit invoice data via myDATA, including suspensions of operations running 48 to 96 hours depending on severity. Since June 1, 2024, economic operators have had to send EN 16931 e-invoices to all contracting authorities in public procurement, and since January 1, 2025 e-invoicing has been mandatory for every General Government expenditure over €2,500.

The digital reporting requirements reach further than the B2B mandate: they cover B2B, B2G and B2C transactions, domestic and international, with no threshold foreseen for companies resident in Greece or subject to local accounting requirements. There is one relief valve. A taxable person with turnover under €50,000 or issuing fewer than 50 invoices per year can use a special data entry form to manually upload invoice data on the myDATA web portal.

The October checklist

1. Confirm you are Phase B. If your gross revenues were €1 million or less in the 2023 tax year, your mandatory date is October 1, 2026. Phase A businesses went through this in the spring; their rollout is a preview of yours.
2. Decide on the adaptation period, then file on time. Businesses with gross revenues up to €1 million (based on the 2023 tax year) can use an adaptation period from October 1 to December 31, 2026, continuing to issue invoices through existing methods in parallel. Using it requires a declaration by October 12, 2026. No declaration is required if, from October 1, 2026, you issue invoices exclusively through Timologio or myDATAapp. One important limit on those clarifications: they cover only the free AADE applications. Businesses using a certified Electronic Invoicing Provider have separate declaration requirements under AADE Decision A.1112/2025.
3. Pick your transmission channel. Businesses must use a certified e-invoicing service provider, AADE's free Timologio application, or direct API integration with myDATA. This is the decision that shapes everything downstream, so make it before October, not during the transition window.
4. Get the format and the codes right. The invoice must be a structured EN 16931 document. myDATA validates submissions against EN 16931 requirements and Greek-specific classification codes covering income categories, VAT categories, invoice types and payment methods.
5. Know what validation returns. When an invoice passes, myDATA assigns a registration number, the MARK, and returns it to the issuer; that MARK must appear on the document you provide to the buyer.
6. Treat data quality as a compliance issue, not a tidy-up. myDATA checks required field completeness, VAT calculation accuracy, classification code validity and format compliance, and whether it accepts or rejects your submissions follows directly from the quality of the invoice data you send. A rejected submission is rework under a deadline.
7. Leave B2C alone. AADE stated in a September 22, 2026 press release that mandatory e-invoicing does not change the obligations or issuance process for receipts and revenue documents in B2C and retail transactions with final consumers.
8. Prepare for the e-invoices you will receive. The mandate reshapes your payables too. Suppliers' structured invoices will arrive alongside the PDFs, photos and scanned receipts Zerentry already reads, and everything ends up in the same ledger.

Where the data-entry layer fits

What Zerentry covers is the document work around the mandate. It reads invoices and receipts that arrive as PDFs, photos or forwarded emails in 50+ languages, with mixed-language support, and extracts the vendor, invoice number, dates, VAT, totals and line items. Every extracted field carries a confidence score, so review goes to the values that actually need a human eye. Duplicate detection compares every new document against your full history, even when the file was renamed or scanned twice, and anomaly detection flags unusual amounts, first-time vendors and missing VAT against your supplier history. Validated data pushes to Xero, QuickBooks or Zoho Books without copy-paste or CSV exports. If your ledger runs on QuickBooks, our guide to QuickBooks invoice automation walks through the sync end to end.

That layer matters in both directions in October. Incoming structured invoices still need checking against your books, and the PDFs, receipts and statements that never touch myDATA still need to become clean data before month-end.

You can test it on the free plan with 30 OCR pages per month. Paid plans start at $29 per month, additional pages beyond your plan cost $0.05 each, and the first 100 workspaces get 50% off the first year with no contract and cancel anytime.

FAQ

When does Phase 2 of Greece's B2B e-invoicing mandate start?

October 1, 2026, for all remaining taxpayers established in Greece, with a transition period through December 31, 2026. Large businesses, those with over €1 million in 2023 revenues, began on March 2, 2026.

Do small businesses get an exemption?

No. Greece's digital reporting system covers all companies resident in Greece with no threshold foreseen. The relief for smaller businesses is procedural: turnover under €50,000 or fewer than 50 invoices per year lets you manually upload invoice data through a special form on the myDATA web portal.

Does the mandate change retail receipts and B2C documents?

No. AADE's September 22, 2026 press release confirmed that the obligations and issuance process for receipts and revenue documents in B2C and retail transactions with final consumers are unchanged.

What format must a compliant invoice be in?

A structured electronic document conforming to EN 16931. Paper and PDF no longer meet the requirement for domestic B2B transactions, and myDATA validates each submission against that standard plus Greek classification codes for income, VAT, invoice types and payment methods.

What is myDATA?

The national platform where electronic VAT reports and e-invoices are submitted and validated. Electronic reporting through it has been mandatory under Law 4646/2019, and entities under Greek Accounting Standards transmit their e-book data to AADE through its REST API.