South Korea has required VAT tax invoices to be electronic for corporations for years, and for individual businesses above a prior-year sales threshold (summaries put it at KRW 80 million since 1 July 2024). The invoice is issued through the National Tax Service's Hometax portal or a certified provider and reported to the NTS by the day after issue.
The free E-invoice Preflight site now has a page for it, with a local check of a 10-digit business registration number's check digit (it catches typos; it looks nothing up). The page says plainly that it was written from memory of secondary summaries and that the statute and NTS notices were not read, so every figure is a lead to check. It is the 51st country page, listed in the by-country hub.