What is a KSeF collective identifier?

A KSeF collective identifier (identyfikator zbiorczy) is a number KSeF generates for a set of at least two structured invoices issued by one seller. From 1 January 2027 it goes into the title of a transfer that pays several invoices at once, in place of their KSeF numbers, and only KSeF can say which invoices it covers (Ministry of Finance).

What does it look like?

It has 35 characters, in the pattern 9999999999-IZRRRRMM-FFFFFFFFFFFF-FF (Ministry of Finance):

The KSeF API specification gives the check: a CRC-8 of the first 32 characters with polynomial 0x07 and initial value 0x00, as for a KSeF number, and the example 1111111111-IZ202607-65ED02180000-E7 (KSeF API specification). So a typo in a title can be caught without asking KSeF, but the invoices behind a correct identifier cannot.

How is it made and used?

To generate one, you declare the list of KSeF numbers it is to cover, in Aplikacja Podatnika KSeF or in software connected to the KSeF API; the issuer or, for example, the buyer can do it. KSeF also decodes it: it shows the KSeF numbers an identifier covers, and for a KSeF number, the identifiers it appears in (Ministry of Finance).

In a split payment (MPP), a buyer paying for e-invoices can choose some of a supplier's invoices rather than all of them for a period, and then gives the collective identifier in the transfer's message instead of the period.

Klarbon recognises a collective identifier in a bank statement and checks its shape and check characters. To match it to invoices, check the KSeF numbers in your payment titles and paste the KSeF numbers it covers, as KSeF lists them.