Greece e-invoicing from 2 November 2026: what to set up first

What the dates mean for you

The second wave is aimed at businesses with 2023 gross revenue up to €1 million. Those with higher revenue started earlier, on 2 March 2026. The start date of 2 November 2026 came from AADE Decision A.1197/2026, which replaced the earlier 1 October 2026 date. Some websites still show 1 October, so check the date against AADE's own page before you plan.

There are three dates to keep in mind. On 2 November 2026 the obligation starts. From 2 November 2026 to 31 January 2027 the transition period lets you keep using your existing accounting software, your ERP or the myDATA special entry form alongside the approved channels. On 1 February 2027 the transition ends, and issuing and sending must run exclusively through a certified provider or the AADE applications. Three days separate this page's date from the first deadline, so the setup work is short and should start now.

What it costs you to leave this until the last week

The main cost is staff time and rework. Suppose your team currently retypes 40 invoices a week into a second system, at about 10 minutes each. That is roughly 6.7 hours a week, or about 27 hours a month. These are planning inputs, not a published figure. Replace them with your own invoice count and your own minutes per invoice.

The second cost is a document that is wrong or not issued correctly. Greek guides describe that a document issued by hand or straight from an ERP, outside the approved channels after the transition, may not count as issued. One third-party guide points to an AADE circular numbered E.2004/2026 for this point, so read that circular on AADE's site before relying on it. Penalty amounts are not set out in the sources reviewed for this guide. Check AADE's e-invoicing pages for the figures that apply to you.

Manual way and automated way

How to automate it, step by step

1. Confirm your wave and your revenue. Check your 2023 gross revenue figure and the date that applies to you on AADE's site. Write the date down.
2. Choose the channel. If you issue only through timologio or myDATAapp from 2 November, no declaration is needed. If you use a certified provider, file the Declaration of Commencement of Electronic Document Issuance in myAADE with a start date of 2 November 2026.
3. Map every route your invoices take today. List each system that creates an invoice: the ERP, a billing tool, a spreadsheet, a cash register. If your ERP sends straight to myDATA through the API, that route closes for domestic B2B on 1 February 2027. Decide now whether it moves to a provider or to a free AADE app.
4. Connect the sending step. AADE publishes REST API documentation for ERP and provider integration. If your ERP vendor or IT person builds the link, they should work from that documentation. Open-source libraries for the myDATA API exist, but they are community projects, not AADE products, and they need the same testing as any other code.
5. Automate the intake of supplier invoices. Use OCR to read PDF invoices and a language model to draft the entry and suggest a classification. Keep a person as the approver. For received invoices, the buyer must apply the AADE classification codes, and the software cannot set them for you.
6. Automate the follow-up. Send issued invoices and payment reminders from the same record that holds the MARK, through email or a WhatsApp Business channel where your customers use it. Keep rejections and disputes in a queue that a person works each morning.
7. Test before 2 November, then run in parallel. Issue a set of test invoices in each route, compare the results with your ledger, and only then switch the live flow. Use the transition to 31 January 2027 to clear the old route, not to postpone the test.

What breaks and how to prevent it

The most common break is a duplicate. If a route sends an invoice, the operator retries, and nobody checks the first attempt, the same invoice can reach myDATA twice. One open-source client for the myDATA API reports error 603, which means the invoice has already been sent. Prevent this by giving each invoice a single unique series and number, and by blocking a resend unless someone confirms it.

The second break is numbering. Series and sequence numbers must run in order. If two systems issue from the same series, gaps and clashes follow. Use one numbering source per series, and stop any system that is no longer in use before the switch.

The third break is a wrong VAT or classification code. Automation copies whatever it is told, so a wrong rate set once will repeat across hundreds of invoices. Review the tax settings for each product group before go-live, and sample a set of invoices each week during the first two months.

The fourth break is a buyer who cannot receive the invoice. One compliance guide notes that buyers must be able to receive and process e-invoices from the issuer's mandatory date. Ask your main customers which channel they use, and keep the email copy as a fallback until the flow is proven.

When not to automate

If you issue only a few invoices a month, the free timologio app may be enough, and a clean manual process is cheaper to run than a connection you must maintain. If your VAT treatment is unusual, for example mixed rates, exports or several entities, fix the rules with your accountant first. Automation does not decide the tax treatment. It repeats it, so a poor rule runs faster and at a larger scale. Also, if your ERP is old and no provider supports it, the cost of a custom link may exceed the saving, and a provider or AADE app is the better route.

Automation also cannot replace the owner's sign-off. Someone must still confirm the tax treatment, approve the rejects and answer the buyer when a document is wrong.

What it typically takes

The work is measured in weeks of attention, not in software purchases. For a business on timologio, the time goes to setting up the customer list, product list, series and test invoices. For a business with an ERP, the time goes to mapping fields, testing the link and training the people who issue documents. The critical window is before 2 November, when the choice of channel and the declaration must be in place. The second window is before 1 February 2027, when any direct ERP route must be gone.

This explains the rule in general terms; it is not legal or tax advice for your case.