Electronic invoicing provider: what you must do before 1 October 2026

From 1 October 2026 you can no longer issue an invoice to another business the way you have until now. Every B2B invoice will be issued in a structured digital format — either through a certified electronic invoicing provider, through the free AADE applications, or directly via its API. The transition period ends on 31 December 2026.

If you are reading this in September, you still have time — but not much. Technical preparation for a small business realistically takes a few weeks, not a few hours.

What exactly changes — and what does not

The most common misconception: myDATA does not change. Your data was already transmitted there and will continue to be. What changes is the method of issue of the document.

Until now you could issue an invoice with your own software, even by hand in some cases, and the data was transmitted afterwards. From 1 October the invoice is created digitally, in a standardised format based on the European standard EN 16931, and transmission to myDATA happens automatically through the same channel.

It does not apply to retail

The obligation applies to B2B transactions, that is between businesses. Retail sales to individuals (B2C) does not are covered by the obligation at this stage. If you have a retail shop and do not issue invoices to businesses, your cash register continues as it is.

Also, for sales to businesses within the European Union electronic invoicing remains optional. The obligation covers domestic B2B transactions and transactions with third countries outside the EU.

Who it applies to and from when

It is applied in two phases, with gross revenue as the criterion:

Mind the criterion. The 1,000,000 euro threshold is judged on the return for the financial year that began within 2023 — not last year’s or this year’s revenue. If you are unsure which phase you fall under, check that specific return and not your current turnover.

In practice, Phase B covers the overwhelming majority of businesses in the Pella region: the freelancer, the retail shop, the workshop, the farming business that invoices wholesale.

The three routes to compliance

1. A certified electronic invoicing provider

It is a company licensed by AADE that issues your documents in the structured format, seals them digitally and transmits them automatically to myDATA. It is the solution for anyone issuing a steady volume of invoices or wanting a link to their commercial software. The official list of certified providers is on the AADE website — always confirm there that the provider you are considering is active.

2. The free AADE applications

AADE provides timologio for desktop and myDATAapp for mobile devices. They meet the obligation at no cost and are adequate for a low volume of documents. Their limitation is that they do not automate: every invoice is entered by hand and they do not connect to commercial software or stock control.

3. Direct connection to the AADE API

This is for businesses with their own ERP or specialised software. It requires technical implementation and is not a realistic option for a small business.

How to choose a provider

We do not recommend a particular company — the right choice depends on how you work. The criteria that genuinely matter:

• Integration with what you already use. If you have a commercial application or an e-shop, integration is the first question, not price.
• The real cost. Ask about the annual subscription, the per-document charge and the initial setup cost. All three together are the cost — not the subscription alone.
• The document types it covers. Invoices, credit notes, delivery notes, self-billing: record what you issue before you ask.
• Support in Greek, from a person. On the day an invoice will not issue, a ticket answered in 48 hours is no use to you.
• Data export. If you change provider tomorrow, you must be able to take your archive with you.

What the transition period really means

From 1/10 until 31/12/2026 you may use the parallel use the existing methods of issue and transmission. This is an adjustment period, not a postponement.

The difference matters: it does not mean you can deal with it in January. It means you have three months to set the system up, learn it and fix mistakes without risking a penalty. From 1/1/2027 the grace period ends.

The penalties

For a document subject to VAT that was not issued lawfully, the penalty amounts to 50% of the tax attributable, with a minimum of 250 or 500 euro per breach depending on the case. For documents without VAT, the penalty ranges from 500 to 1,000 euro.

The critical point is that the penalty is imposed per document. In a business issuing dozens of invoices a month, one uncorrected omission does not cost 250 euro — it multiplies.

There are tax incentives too

The law provides enhanced deductions for those investing in electronic invoicing: enhanced depreciation of equipment and software in the year of purchase, plus an uplift on production and transmission costs for the first twelve months.

The incentives are tied to early adoption relative to the mandatory date, so eligibility is assessed case by case and it depends on exactly when you started. If you have already invested in a provider or software during 2026, it is worth checking whether your costs qualify — it is not automatic and it does not apply to everyone.

What to do during September

1. Confirm which phase you fall under, based on the return for the 2023 financial year.
2. Record what you issue today: document types, monthly volume, who they are addressed to.
3. Choose your route: a provider if you have volume or integrations, a free AADE application if you issue few invoices.
4. Run a real test issue before 1 October. Not a demo from the supplier — your own invoice, to your own customer.
5. Inform your accountant about which route you chose, so the flow to myDATA can be adjusted.

See the remaining fourth-quarter deadlines in the tax calendar.

Frequently asked questions

I am a freelancer and issue 5 invoices a month. Do I need a provider?

Not necessarily. The free AADE applications, timologio and myDATAapp, meet the obligation and are adequate for a small volume of documents. You need a provider when you want automation or a link to other software.

I have a retail shop. Does it apply to me?

Only for the invoices you issue to businesses. Retail receipts to individuals are not covered by the obligation at this stage.

What if I am not ready by 1 October?

Until 31 December 2026 a transition period applies during which the existing methods of issue may be used in parallel. From 1/1/2027, however, non-compliance carries penalties per document.

Does anything change in myDATA?

Not to the transmission obligation. What changes is the channel: with electronic invoicing, transmission happens automatically from the provider or the application, with no separate step.

I invoice clients in another EU country. Does it apply to them too?

For businesses within the EU, electronic invoicing remains optional. The obligation covers domestic B2B transactions and transactions with third countries outside the EU.

How do I know whether a provider is certified?

Only from the official AADE list of certified providers. Do not rely on the supplier’s own claim.

If you want this sorted without the stress

At our office in Giannitsa we help businesses across the Pella region choose the route that suits their own volume and way of working — and test it before it becomes compulsory, not in the final week. See our our VAT and myDATA services or get in touch with us.

This is for information only and does not replace individual advice. Deadlines and technical specifications change by decision of the Ministry of National Economy and Finance and of AADE — always confirm the rule in force for your own case.