MARK: the myDATA Unique Registration Number

MARK is the unique registration number that myDATA returns for every document successfully transmitted to it. A document is considered registered in the electronic books only once it has received a MARK.

AADE defines it as the number it assigns to every valid data transmission to the myDATA platform (decision Α.1138/2020). Put simply, MARK is AADE's "receipt": it tells you the document's data arrived, passed the checks and was registered.

You will also find the term in the e-invoicing glossary, alongside the other myDATA terms.

A MARK is assigned the moment myDATA accepts a transmission. The process is:

1. You issue the document in your invoicing software.
2. The software, or a certified provider, transmits its data to myDATA.
3. myDATA checks the data. If it is valid, it returns a MARK. If not, it returns an error and no MARK is assigned.

So a document without a MARK has not been registered, even if you have printed it or sent it to the customer. That is why it is worth checking that every document you issue has one.

• Identification in myDATA. MARK identifies a specific document on the platform, for both the issuer and the recipient.
• Linked documents. A credit note for a specific invoice references the MARK of the original, so myDATA knows which document it corrects.
• Recipient classifications. A business receiving an invoice sees it in myDATA by its MARK and records its own expense classifications against it.
• On the document. The MARK is usually printed on the document, together with a QR code and, on provider documents, the UID.

myDATA builds a business's electronic books from registered documents, that is, from those with a MARK. A document that was issued but never got a MARK is missing from your income as AADE sees it, and may show up as a discrepancy when your customer records the matching expense.

In practice, then, the MARK is the quickest sign that everything went through. If it is missing, look at the error myDATA returned, fix the data and transmit again.

A MARK is never really lost: it is registered in myDATA. According to AADE's FAQ, you can search for the document on the platform by criteria such as its issue date. If your invoicing software stores the MARK on each document, you will not even need to.

A document that has received a MARK is not "deleted". If it needs correcting, a credit note linked to the original's MARK is usually issued. Where cancelling the transmission is allowed, the cancellation is itself recorded in myDATA with its own number. The right way to correct depends on the case, so check with your accountant.

MARK is assigned by AADE after transmission. The UID is calculated from the document's own data (issuer VAT number, date, branch, type, series, number) and identifies the document regardless of transmission. MARK says "registered"; UID says "which document this is".

In eFluper every document is transmitted to myDATA when you issue it (or manually, if you prefer) and comes back with a MARK and QR code. When you issue through the certified provider, the document carries the MARK, UID and authentication code, plus a QR code the customer scans to verify it. Read more in what is myDATA.