Thai finance teams running ERPNext hit the same wall every filing period: core ERPNext ships a generic tax engine and Gregorian-only dates, so Thailand's 7% VAT split between output and input tax, the withholding-tax (WHT) certificates required under PND 3, PND 53 and PND 54, Buddhist-era (B.E.) date formatting, and bilingual Thai/English tax invoices all end up handled in spreadsheets or bolted on with fragile customizations. The Revenue Department (RD) expects specific document formats and a sequential, gap-free tax-invoice numbering trail that stock ERPNext does not enforce, and a single mis-issued WHT certificate means a supplier cannot reconcile their own filing.

ECOSIRE builds a proper Frappe app — a versioned, installable module rather than a pile of in-site customizations — that layers Thai compliance onto ERPNext without forking core. We ship a Withholding Tax Certificate DocType (PND 3/53/54 variants) that pulls the payee's Tax ID, income type and WHT rate straight from the linked Payment Entry or Purchase Invoice, so the certificate is generated at source instead of re-keyed. VAT is modeled with dedicated 7% output/input Item Tax Templates and Tax Categories, plus a server-side hooks.py doc-event (on_submit) that stamps a sequential Thai tax-invoice number and validates the counterparty Tax ID before submission. Buddhist-era dates are handled with a reusable formatter applied through custom print formats and a client script, so the same posting date renders as B.E. on Thai documents and C.E. on internal reports. Bilingual invoices, receipts and WHT certificates are delivered as Thai/English print formats with correct Thai numeral and Baht-in-words rendering.

Reporting is built to line up with what the RD and your auditor actually ask for. We deliver Query/Script Reports for the VAT output and input tax summaries (Por Por 30 basis) and a WHT summary keyed by PND form and payee, exposed to a dedicated Thai Tax role profile so finance officers see the reports and controls without touching system settings. Where you need programmatic access — a filing portal, an external tax connector or a scheduled export — the certificates and summaries are reachable through the Frappe REST API and purpose-built @frappe.whitelist() methods, and a scheduler event can batch-generate month-end WHT certificates and flag any Payment Entry that was submitted without the required withholding line.

Because this is build-to-order, nothing is a shrink-wrapped download. After a short scoping call we confirm exactly which PND forms, VAT scenarios and document layouts you need, build against your ERPNext version (Frappe/ERPNext v15 or v16), and hand over installable source plus a git repository. Typical delivery is 2–4 weeks from confirmed scope; we validate on a staging copy of your site (UAT) with a rollback plan before touching production, then run a post-go-live support window so your first live VAT and WHT cycle is covered.