From 1 January 2027, split-payment bank transfers for KSeF invoices must carry the 35-character KSeF number instead of the seller's own invoice number; using it before then is voluntary.
Why It Matters
There is no direct fine for getting it wrong, but an incorrect or missing KSeF number will break automatic matching between the payment and the invoice on both sides once the rule takes effect. The result is manual reconciliation and payment delays, not a bounced transfer, and it will hit every VAT invoice your firm pays by split payment from that date onward.
What To Do About It
You have until January 2027, use it. Ask your accounting software or bank now whether the KSeF number can already populate the transfer title field for split-payment invoices, most systems still need a manual update for this. Start using it voluntarily this year so the switch is not a scramble.
Sources
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