Korean VAT law requires corporate taxpayers and most individual businesses to issue electronic tax invoices and transmit them by the day after issuance, with penalties assessed per invoice for late or missing transmission. Dynamics 365 Business Central posts a sales invoice, produces a document number, and stops there. There is no Korean business registration number (사업자등록번호) structure on the customer card, no distinction between a 세금계산서 and a 계산서 for exempt or zero-rated supply, no NTS-shaped payload, no transmission state on the posted document, and no place to record the approval number (승인번호) the National Tax Service returns. Finance teams close the gap with an operator keying invoices into Hometax by hand, or an ASP screen that lives outside the ERP — either way the ledger and the tax filing drift apart, and the quarterly VAT return becomes a spreadsheet reconciliation exercise.

ECOSIRE builds an AL extension that makes the e-tax invoice a first-class part of the posting flow. Table and page extensions add the Korean fields Business Central lacks: business registration number with checksum validation, sub-business (종사업장) code, taxation type per line, and supply amount and VAT amount held separately as the NTS schema expects. A Korea E-Tax Setup page holds environment (test or production), channel credentials, certificate references, the issuance numbering series, and the mapping rules. Event subscribers on sales posting create a queued e-tax invoice record; a builder codeunit assembles the payload from posted lines and applies the tax mapping; a connector codeunit transmits it to your certified ASP or Hometax-facing gateway over HTTPS using credentials held in Isolated Storage in your own tenant — your tax data does not route through ECOSIRE infrastructure. A job queue entry polls for status and writes the approval number, NTS timestamp, and result code back onto the posted invoice, so a finance user sees Issued, Accepted, or Rejected on the document they already work from.

One posting produces both outputs. The machine format is the structured payload the tax authority receives; the human-readable format is a Business Central report layout of the Korean tax invoice rendered from the same record, so the PDF the customer receives can never disagree with what was filed. Rejections are treated as work, not as an error log: a rejected invoice lands in a Korea E-Tax Invoice list with the NTS result code translated into plain language, and a correction action creates the appropriate corrective document (수정세금계산서) carrying the statutory correction reason and a link back to the original approval number, so the chain stays traceable at audit. Cancellation, amount change, and buyer-detail correction each map to their own reason code rather than collapsing into a generic credit memo.

Archiving is built for the long statutory retention period Korean practice expects. Every transmission, response, and correction is written to an immutable log table with the exact payload bytes, timestamp, and the user who triggered it; the log is exposed through a dedicated API page (REST API v2.0 / OData v4) so an auditor extract, a Power BI report, or a Dataverse-connected review app can read it without a database export. Permission sets separate the accountant who issues from the administrator who configures the channel, and telemetry is emitted to your Application Insights so a failed transmission surfaces as an alert rather than as a surprise at filing time.

This is a build-to-order engagement, not an AppSource download. We start with a scoping call to confirm your Business Central version and deployment (SaaS or on-premises), your ASP or gateway of choice, which supply types you actually issue, and how your customer master carries registration numbers today. From confirmed scope, typical delivery is one working week: we build against your release wave, install into a sandbox, run UAT with your finance team over real document flows including a deliberate rejection and correction cycle, then deploy to production with a rollback plan. You receive the AL source, the git repository, and a post-go-live support window.