- 28
- March
Many organizations already understand what e-Tax Invoice is, but when it comes to actual implementation, they don't know where to start, what documents to prepare, which channels to register through, or what to do after registration. This article is a complete step-by-step guide that walks you through the entire process — from choosing the right system, registering, to successfully issuing your first electronic tax invoice.
Quick Summary: Thailand's Revenue Department offers 2 e-Tax Invoice systems — the full system (using Digital Signature) for all VAT-registered businesses, and the Email system (using Time Stamp) for businesses with annual revenue not exceeding 30 million baht. Both register through etax.rd.go.th
2 e-Tax Invoice Systems — Which One to Choose?
Before registering, you need to understand that Thailand's Revenue Department divides e-Tax Invoice into 2 distinct systems:
| Details | e-Tax Invoice & e-Receipt (Full System) | e-Tax Invoice by Email |
|---|---|---|
| Eligibility | All VAT-registered operators | Annual revenue not exceeding 30 million baht |
| Document Authentication | Digital Signature (Certificate from authorized CA) | Time Stamp from Revenue Department's system |
| File Format | PDF/A-3 + XML | PDF sent via email |
| Data Submission to Revenue Dept. | Submit XML through the system | Automatic submission via email |
| Initial Cost | Digital certificate fee (~3,000-15,000 baht/year) | No additional cost |
| Best For | Medium-large organizations issuing many tax invoices | SMEs wanting a simple start |
Recommendation: If your organization's annual revenue is under 30 million baht and you don't issue many tax invoices, we recommend starting with e-Tax Invoice by Email — it's easy to register with no need to purchase a Digital Signature. However, if your organization plans to grow or already uses an ERP accounting system, you should go directly with the full system.
e-Tax Invoice by Email Registration — Step by Step
For SME operators with annual revenue not exceeding 30 million baht, you can register for the e-Tax Invoice by Email system following these steps:
- Visit the Revenue Department website — Go to etax.rd.go.th and select "e-Tax Invoice by Email"
- Enter your Tax ID number — Input the 13-digit tax identification number along with branch information
- Fill in operator information — Company name, address, email for sending/receiving tax invoices
- Print and sign Form Kor.Or.01 — The system generates the form automatically; print it and have it signed by an authorized director
- Scan and upload documents — Scan the signed Kor.Or.01 form along with supporting documents and upload to the system
- Wait for Activation Code by mail — The Revenue Department sends an Activation Code to your registered address (approximately 7-15 business days)
- Confirm Activation Code — Log into the system and enter the Activation Code to activate your account
Required Documents for e-Tax Invoice by Email
| No. | Document | Notes |
|---|---|---|
| 1 | Form Kor.Or.01 | Signed by authorized director + company seal (if applicable) |
| 2 | Company Certificate | Issued within the last 6 months |
| 3 | Copy of Por.Por.20 | VAT registration certificate |
| 4 | Copy of Director's ID Card | The person who signs the Kor.Or.01 form |
e-Tax Invoice & e-Receipt (Full System) Registration
For organizations that need the full system — which supports high-volume tax invoice issuance and direct integration with accounting systems or ERP — follow these steps:
- Obtain a Digital Certificate from an authorized CA — Choose a Certificate Authority (CA) authorized by the Revenue Department
- Install the Digital Signature — Install the digital certificate on your organization's computer or server
- Register at etax.rd.go.th — Select "e-Tax Invoice & e-Receipt" and fill in your operator details
- Submit documents — Form Kor.Or.01, company certificate, copy of Por.Por.20, power of attorney (if applicable)
- Test XML submission — Test sending XML files in the Revenue Department's required format through the Sandbox environment
- Wait for approval — The Revenue Department reviews and approves (approximately 15-30 business days)
- Go live — After approval, you can immediately start issuing electronic tax invoices
Authorized Certificate Authority (CA) Providers
| CA Provider | Certificate Type | Approximate Cost |
|---|---|---|
| TDID (Thai Digital ID) | Organization Certificate | ~5,000-15,000 baht/year |
| TOT CA | Organization Certificate | ~3,000-10,000 baht/year |
| CAT CA | Organization Certificate | ~3,000-10,000 baht/year |
After Registration — What's Next?
Successful registration is just the beginning. The actual e-Tax Invoice workflow involves the following steps:
| Step | Description | Full System | Email System |
|---|---|---|---|
| 1. Issue Tax Invoice | Create a tax invoice in electronic format | PDF/A-3 + XML | PDF via email |
| 2. Apply Digital Signature | Sign the document electronically for authentication | CA-issued certificate | Automatic Time Stamp |
| 3. Send to Buyer | Deliver the tax invoice to the customer | Send PDF file/email | Auto-sent via email |
| 4. Submit XML to Revenue Dept. | Submit tax invoice data to the Revenue Department | Via API/Upload | Automatic submission |
| 5. Document Retention | Store electronic documents as required by law | Must retain for at least 5 years in both systems | |
Important: The law requires electronic documents to be retained for at least 5 years from the date of issuance. Failure to comply may result in penalties under the Electronic Transactions Act. Using an ERP system with a comprehensive accounts payable module and accounting helps organize document storage systematically.
Common Mistakes When Registering for e-Tax Invoice
From our experience consulting with numerous clients, we've identified these recurring mistakes:
| Problem | Cause | Solution |
|---|---|---|
| Activation Code not received | Address in Por.Por.20 doesn't match current address | Verify and update the address in Por.Por.20 before applying |
| XML validation failure | XML format doesn't comply with Revenue Dept. specifications | Test through Sandbox first and use the latest schema from the Revenue Department |
| Expired Digital Signature | Digital certificates are valid for 1-2 years and need renewal | Set a calendar reminder 1 month before expiration |
| Email not reaching customers | Emails going to spam or being blocked | Use company domain email and configure SPF/DKIM properly |
| Expired company certificate | Using a certificate older than 6 months | Obtain a new certificate from DBD before submitting the application |
Integrating e-Tax Invoice with ERP — Full Automation
Issuing e-Tax Invoices separately from your accounting system causes multiple problems: duplicate data entry, mismatched document numbers, and difficult audit trails. Integrating with an ERP system solves all of these issues.
| Manual (Separate) | ERP (Automated) |
|---|---|
| Re-enter tax invoice data every time | Auto-pull data from delivery orders/invoices |
| Track document numbers manually | Automatic running numbers — no duplicates |
| Export XML separately | Auto-generate XML in Revenue Dept. format |
| Store documents separately from accounting | Stored in one system — easy to search and audit |
| Reconcile input/output tax manually | Tax reports generated automatically |
Saeree ERP supports e-Tax Invoice issuance directly from the system — no duplicate work required. Data from the accounts payable module, accounting system, and PDPA-compliant data management are fully integrated end-to-end.
e-Tax Invoice is not just a Revenue Department requirement — it's an opportunity to digitize your entire document issuance process. When integrated with a good ERP system, it reduces manual work, minimizes errors, and ensures audit readiness from every agency.
— Sureeraya Limpaibul, Saeree ERP
Summary — Checklist Before Starting e-Tax Invoice
| ✔ | Item |
|---|---|
| ☐ | Decide on system: Full system or by Email |
| ☐ | Prepare documents: Form Kor.Or.01, Company Certificate (within 6 months), Copy of Por.Por.20 |
| ☐ | Obtain Digital Certificate from CA (full system only) |
| ☐ | Register at etax.rd.go.th |
| ☐ | Test XML submission through Sandbox (full system only) |
| ☐ | Confirm Activation Code / Wait for approval |
| ☐ | Integrate with ERP/accounting system for automated e-Tax Invoice issuance |
| ☐ | Establish a 5-year electronic document retention policy |
If your organization is planning to implement e-Tax Invoice and needs an ERP system that supports end-to-end electronic tax invoice issuance, you can schedule a demo or contact our consulting team to assess your organization's readiness.
