E-invoicing from 1 October 2026, and what changed in Stripe and Google Calendar for booking businesses

From 1 October 2026, two weeks from the date of this article, electronic invoicing becomes mandatory for every Greek business that was not already covered by the first phase in March. If you issue invoices to other businesses, such as travel agencies, hotels, schools or clubs, those invoices will need to go through a certified provider or AADE's own free apps. Your accountant can confirm exactly which of your documents are covered.

Around it sit smaller changes for anyone who takes bookings and payments: IRIS, card terminals, Stripe fees in Greece, and new Google Calendar limits. We say plainly where the answer belongs to your accountant, not to us.

What changed

E-invoicing (myDATA). According to AADE's official FAQ:

• Businesses with gross revenue over €1,000,000 in their 2023 income tax return have had to issue e-invoices since 2 March 2026.
• All other businesses must do so from 1 October 2026.
• From 1 October to 31 December 2026 a business can still use other ways of issuing and transmitting invoices while it moves over, provided it has filed a declaration of commencement of electronic issuance with a start date no later than 1 October 2026.
• E-invoices are issued through a certified e-invoicing provider, or through AADE's free applications, timologio and myDATAapp. Accounting or ERP software on its own is not an accepted way to issue them.
• Not issuing an e-invoice is treated as not issuing an invoice at all, with the penalties the Tax Procedure Code sets for that.

IRIS and receipts. In its 17 November 2025 announcement, AADE set 1 December 2025 as the date from which businesses selling to consumers must accept IRIS payments. It restated the principle that a payment by card or IRIS means a receipt must be issued from the cash register system.

Card terminals and the cash register. Under AADE's circular E.2044/2024 (announcement of 20 June 2024), every retail business that must use a cash register has to connect all its card terminals to it. Businesses that only sell wholesale are exempt. Taking a payment on a terminal that is not connected carries a fine of €10,000 or €20,000, depending on the business's accounting system.

Stripe in Greece. Stripe's published prices for Greek accounts are 1.5% + €0.25 for standard cards from the European Economic Area, 2.8% + €0.25 for premium ones, and 3.15% + €0.25 for international cards (Stripe pricing). Revolut Pay costs the same as a standard card, 1.5% + €0.25. Klarna costs 4.99% + €0.40 (local payment methods). IRIS is not a built-in Stripe option. Stripe supports it only through its Custom Payment Methods feature (Stripe on IRIS).

Google Calendar. From 1 May 2026, Google applies new limits on how often software can use Google Calendar. Projects that already used it between November 2025 and April 2026 keep their previous limits. Google says that going over the limits "is planned to incur charges to your Google Cloud billing account later in 2026" (Calendar API usage limits). It has not said when, or how much.

What it means for your business

E-invoicing is the deadline that cannot slip. If your booking system produces invoices for agencies, hotels or group bookings, those invoices will have to be issued through a certified provider or AADE's apps from 1 October 2026. The booking system alone does not count, though it can usually prepare the data and pass it to a provider. Whether that link exists is a question for your developer. Whether the transition declaration is filed is a question for your accountant.

Online deposits still need the right documents. Being paid through a Stripe payment link does not, on its own, take care of the paperwork. What must be issued for a deposit taken online, when, and from which system, is a question for your accountant, not us. Give them a real example: a deposit taken in March for a dive in July.

IRIS through Stripe takes extra work. Stripe's own page presents showing IRIS at checkout as a compliance duty for Greek businesses from 1 December 2025. On Stripe, that means adding IRIS as a custom payment method, and sending every IRIS payment's receipt or invoice to myDATA. Ask your accountant whether it applies to your online checkout before you build it.

Klarna costs a lot more than a card. On a €400 booking, a standard card costs €6.25 in Stripe fees and Klarna costs €20.36. Only offer it where larger bookings justify it.

Calendar sync should keep working for systems that were already using it between November 2025 and April 2026. New ones should use Google Calendar sparingly, because Google plans to charge for heavy use.

What to do before 1 October

1. Call your accountant this week. Ask whether the declaration for the transition period has been filed, and which provider or AADE app your invoices will go through.
2. Ask your developer whether your booking or ticketing system issues invoices itself, and if so, how it will connect to that provider.
3. Ask your accountant about online deposits: what document is issued, when, and how it reaches myDATA.
4. Walk round the shop and confirm every card terminal is connected to the cash register, including the spare kept for busy days.
5. Check which Stripe payment methods you offer and what each costs.
6. If you run a custom booking system with Google Calendar sync, ask your developer whether it predates 1 May 2026 and how many calendar requests it makes.

If your booking system needs to talk to an e-invoicing provider, that is the kind of work we do. The dive centre system we built takes Stripe payment links and syncs two ways with Google Calendar.

For the technically minded

• The transition declaration is made under Article 6 of Decision A.1112/1.8.2025.
• Stripe's IRIS page lists three duties: declare the business IBAN to AADE, show IRIS at checkout (QR code or redirect), and transmit each IRIS payment's receipt or invoice to myDATA.
• Google Calendar API quotas from 1 May 2026: 10,000 requests per minute per project, 600 per minute per user, 1,000,000 per day per project. Projects with API usage between November 2025 and April 2026 keep their existing quotas.