Two things to check before you start
First: only VAT-registered operators may issue a tax invoice. If you are not registered for VAT, what you give clients is a receipt, not a tax invoice. Issuing one without the right to do so carries penalties. Do not skip this.
Second: the Revenue Department's electronic system covers receipts as well as tax invoices, so anyone with a duty to issue receipts can also use e-Tax Invoice & e-Receipt.
Step 1: pick the right system from the start
Two paths, and they are very different.
e-Tax Invoice by Email — right for most freelancers
- For VAT-registered operators with annual revenue not exceeding THB 30 million
- No electronic certificate required, no digital signature to buy
- Uses PDF/A-3 files, no XML
- The Electronic Transactions Development Agency (ETDA) applies the time stamp
- Free to use
- Register with form Kor Or 01 through the Revenue Department system at interapp3.rd.go.th
- You must not already be approved for, or under review for, e-Tax Invoice & e-Receipt
e-Tax Invoice & e-Receipt — for larger operations
- Required once annual revenue exceeds THB 30 million
- Needs an electronic certificate from an accredited CA provider
- Apply with form Bor Or 01, verifying identity via the Ultimate Sign & Viewer application
- Documents must be produced as standard-format XML for submission
- Data is submitted to the Revenue Department by the 15th of the following month, for example by uploading XML at etax.rd.go.th
If you are a solo freelancer who has just registered for VAT, start with by Email. You can move later.
Step 2: register with Kor Or 01
- Go to interapp3.rd.go.th and choose the Kor Or 01 submission
- Enter your tax ID, business details, and — most important — the email address you will send tax invoices from
- Use an address you genuinely control and will not change soon. The system will not time stamp documents sent from an address that fails verification
- Wait for approval and receive your system password
The same portal has menus for password recovery and for cancelling your time-stamp issuing rights. Bookmark it.
Step 3: build the file to spec
This is where most first attempts fail.
- One document per file. Never bundle several invoices into one PDF
- Maximum file size 3 MB
- PDF/A-3 format only
- No photographs or scans of paper documents. The file must be generated digitally from the start
- Content must include everything a full tax invoice requires: the words tax invoice, both parties' names, addresses and tax IDs, document number and date, description of goods or services, value, and the VAT amount shown separately from the price
Step 4: send the email correctly
- Send only from your registered email address
- Put one buyer address in the To field
- CC the time-stamp system at csemail@etax.teda.th — confirm the current address at etax.teda.th before your first send
- Format the subject line exactly as specified. Tax invoices use the issue date, then INV, then the document number. Debit notes use DBN and credit notes use CRN, each referencing the original tax invoice number
- Attach the PDF/A-3 and send
- Wait for the confirmation email showing the document has been time stamped. Both you and your client receive it
No confirmation means the document is not complete. Check three things first: sender address, subject format, file type.
Step 5: store and submit
- Retain both the document file and the time-stamped confirmation email for the period the law requires
- Keep monthly folders and name files by document number so you can retrieve them later
- On the time-stamp route, data flows to the Revenue Department automatically by email once ETDA stamps it. On the digital signature route, you submit yourself by the 15th of the following month
Cancelling and correcting
From 1 June 2023 the email cancellation procedure changed, and tax invoices, debit notes and credit notes can no longer be cancelled the old way. Check the current procedure at etax.teda.th before you attempt anything.
In practice, prevention beats correction. Verify the client's name, address and tax ID against their company certificate before sending, because fixing a sent document is always more work than checking an unsent one.
Incentives currently available
The tax measure supporting electronic tax systems allows a double deduction on actual spending for e-Tax Invoice and e-Receipt investment, running from 1 January 2026 to 31 December 2027. Over the same period, payments made through e-Withholding Tax use a reduced 1 percent withholding rate. Confirm the current conditions with the Revenue Department before claiming.
The mistakes that keep repeating
- Sending from an unregistered email address
- Photographing a paper document and converting it to PDF
- A subject line that does not match the required format, so nothing gets stamped
- Files over 3 MB, usually from a high-resolution logo
- Duplicated or skipped document numbers
- Missing a change in the client's VAT branch code, so your document does not match what they file
Doing this in MANA
If your documents already live in MANA, the sequence collapses to this: issue the tax invoice from the existing invoice without retyping client details, let the system keep document numbering continuous, export the file and send it into the time-stamp flow, then keep the document attached to the same project and contact.
When the Revenue Department or your client's accounting team asks about a specific job, you open that job. You do not spend an afternoon searching a year of email.