Thai VAT registrants who opt into e-Tax Invoice & Receipt carry an obligation that native ERPNext was never designed for. Core ERPNext gives you a Sales Invoice, a print format and a Sales Taxes and Charges Template — it does not produce a digitally signed electronic document in the structured format the Revenue Department expects, it has no concept of a signing certificate or timestamp, no submission and acknowledgement lifecycle, no rejection-and-correction path, and no tamper-evident archive that survives a records inspection. Finance teams fill that gap with a spreadsheet, a third-party portal and a lot of re-keying: the invoice is posted once in ERPNext, then typed again somewhere else, and the two versions drift. The month you are audited is the month that drift becomes expensive.

We build a proper Frappe app — its own repository, its own module, migrated with bench migrate like any other app — rather than a pile of loose customizations that a version upgrade wipes out. The app introduces DocTypes for the compliance layer: a Thailand E-Tax Settings single for the company profile, tax ID, branch code and issuing options; a Thailand E-Tax Certificate holding the signing credential reference and validity window; and a Thailand E-Tax Document that is the per-transaction record of what was generated, signed, delivered and acknowledged, with its own workflow states and a link back to the source Sales Invoice or Payment Entry. Nothing about the accounting posting changes — your GL, VAT reports and receivables stay pure ERPNext.

Generation hangs off hooks.py doc events. on_submit of Sales Invoice enqueues document generation on the Frappe background worker so the user is never blocked by a signing or network round trip; the tax mapping is derived from your existing master data (Customer tax ID and branch, Item tax templates, Sales Taxes and Charges rows) rather than re-entered, and a validate hook fails the submit early with a clear message when a mandatory Thai field is missing — a missing customer tax ID should stop the invoice, not the filing. One posting yields both outputs: the machine-readable structured document for the authority, and the human-readable PDF built from a dedicated Frappe Print Format so the customer sees the same numbers, with both artifacts attached to the record as File documents.

Digital signing is applied to the generated document before delivery, with the certificate handled server-side and never exposed to the browser. A scheduler event polls outstanding submissions and reconciles status; a rejection creates a linked correction document and reopens the workflow with the reason recorded, so nobody has to guess why a document bounced. Delivery to the customer runs through Frappe's Email Queue with the artifacts attached. Access is controlled by dedicated roles and a role profile — an AP clerk can generate and view, only a Tax Officer can sign or void — and whitelisted methods plus the standard Frappe REST API let an external portal or an in-house tool trigger generation and read status without database access. Client scripts add the buttons and status indicators to the Sales Invoice form so the whole thing lives where your finance team already works. Built and regression-tested for Frappe/ERPNext v15 and v16.

This is build-to-order, not a marketplace download. You request a quotation, we run a short scoping call, and we confirm scope in writing: which document types you issue, your certificate and service-provider arrangement, branch structure, delivery channels and any print-format requirements. From confirmed scope, typical delivery is two to four weeks. We build against your ERPNext version, deploy to a staging site for UAT with your own invoices, then go live with a rollback plan. You receive the full source code and the git repository — the app is yours, and you are never locked to us to keep it running.