In the case of a credit note, the Sequential number of the original invoice is retrieved for the Slovak Kontrolný výkaz (VAT Control Statement) through a link to the original invoice. The Sequential number of the original invoice field is populated with the variable symbol (VS) of the original received invoice or the internal number of the original issued invoice.
A credit note created via Services -> Create Credit Note automatically receives a link to the original invoice. Alternatively, you can create a link to the original invoice by selecting the credit note line and going to Services -> Create/Cancel Credit Note Link.