Since 1 October 2026, every Greek business that issues invoices to other businesses must issue them electronically, through a certified e-invoicing provider or AADE's free applications, after larger companies were brought in from February 2026. That turns invoice data into structured records that AADE's myDATA platform sees almost immediately, and it is exactly what makes AI useful in the back office. An AI system can read supplier invoices, match them to orders and payments, compare your books with what myDATA received, and explain every mismatch in plain language. The arithmetic stays in code, and the accountant still approves and submits.
What changed with mandatory e-invoicing in Greece in 2026?
Mandatory business-to-business e-invoicing changed how every Greek company issues invoices. Businesses with turnover above EUR 1 million had to switch from 2 February 2026 (taxheaven). Businesses with gross revenue up to EUR 1 million followed on 1 October 2026, with a transition period to 31 December 2026 in which the previous methods can still be used in parallel, under decision A.1128/2025 (Ta Nea, August 2026). Invoices must be issued only through a certified e-invoicing provider or AADE's free applications, timologio and myDATAapp. Issuing any other way counts as not issuing the invoice at all, and for invoices subject to VAT the penalty is 50% of the VAT involved, with a minimum per inspection.
What is myDATA, in plain terms?
myDATA is AADE's digital platform that receives the data of Greek businesses' invoices and their income and expense classifications. When both sides of a transaction report it, the tax authority can compare what the seller declared with what the buyer recorded. For a business, that means differences between its own books and what its suppliers transmitted are visible to the authority, and they have to be found and explained before someone else finds them. Details and official guidance are on AADE's myDATA page.
Where do mismatches between the books and myDATA come from?
Mismatches between the books and myDATA come from a handful of recurring causes, most of them on the supplier's side:
- an invoice that the supplier never transmitted, or transmitted late;
- a wrong tax number (ΑΦΜ) or VAT amount on the supplier's record;
- credit notes and cancellations recorded on one side only;
- the same invoice recorded twice, or split differently;
- classification differences between how the supplier and the buyer described the transaction.
Each is simple to understand and tedious to find by hand, because it means comparing hundreds of lines every month across the ERP, the bank and the platform.
What can AI automate in myDATA reconciliation?
AI can automate the reading, matching and explaining, which is where the hours go. A reconciliation agent built for a Greek business typically:
- Reads incoming invoices from email, PDF, scans and XML, and extracts supplier, tax number, date, net amount, VAT and lines, validating the tax number's check digit.
- Matches each invoice to its purchase order, delivery and payment.
- Compares the books with what myDATA received, line by line, and lists every difference.
- Explains each difference in a sentence an accountant can act on: "not transmitted by the supplier", "VAT differs by EUR 23.40", "credit note missing on our side".
- Proposes an expense classification for new invoices, for the accountant to confirm.
- Drafts the email to the supplier asking for a correction, for a person to send.
This is one of the least adopted uses of AI in Greece: in ELSTAT's 2025 count, 521 Greek companies with ten or more staff used AI for accounting or finance, against 2,280 for IT security (AI adoption in Greece).
What must stay out of the AI's hands?
Three things must stay out of the AI's hands in bookkeeping. First, the arithmetic: totals, VAT and differences are computed in code, and the language model only reads documents and explains results. Second, the submission: the accountant or the responsible person approves and files, because a wrong transmission to the tax authority is an expensive mistake to reverse. Third, silent corrections: the system flags and proposes, it never edits the books on its own. Every action and every proposal is logged, so the monthly close has an audit trail. This is the same approval principle I apply everywhere, described in human in the loop.
What does the software for this cost?
The software for this is hard to price from the outside, and that is itself a finding. When I tried to price a year of selling online in Greece using only published prices, the mandatory half of the bill, accounting software, ERP and e-invoicing, had no published price at any of the four major Greek business-software vendors I checked (The Greek SME digital bill). Budget separately for them and ask for written quotes. The AI layer on top is usually the smaller cost: reading and matching a month of invoices costs little in model tokens compared with the hours it saves, and the main work is connecting it to your ERP and your bank.
What does a myDATA reconciliation system look like in practice?
A myDATA reconciliation system in practice is a monthly routine that produces a short list instead of a long hunt. The agent pulls the month's invoices, bank movements and myDATA records, matches what it can, and hands the accountant a list of differences, each with its explanation, the documents behind it and a proposed action. I built a working version of this as one of my ten demo systems, running on synthetic data and labelled as such. The department view is on AI for finance and accounting. Other places where AI pays back first are in AI use cases for small businesses.
Frequently asked questions
Can an AI system submit data to myDATA on its own?
Technically, software can transmit data through AADE's interfaces with the business's credentials. I recommend that a person approves every submission, because the AI's job is to find and explain differences, and a wrong transmission is costly to correct.
Does AI replace the accountant?
No. It removes the hunting and matching, so the accountant spends time on the differences that matter and on advice. The responsibility for the books and the filings stays with the accountant.
Does it work with Greek invoices in PDF or scanned form?
Yes. Modern models read Greek invoices from PDF and scans well, and every extracted value is validated in code, from the tax number's check digit to the totals, before it is used.
If your monthly close includes hours of comparing invoices, bank lines and myDATA, tell me how many invoices you handle a month and which ERP you use.