TDAC not working: what each error message means

Checked 5 November 2026 by Darius Cheung. Independent guide, not a government website.

Short answer

The TDAC site has four general error messages. "We couldn't verify your request" means wait and retry. "Your session has timed out" means start again. "The system is busy" means the server is struggling, so try later. If nothing works, you can still finish at the airport: the embassy says the TDAC can be completed until you reach immigration, and five airports have kiosks.

The site's own messages

These are copied from the English text the TDAC site ships to your browser. The site maps each one to a type of failed request, so the wording tells you more than it seems to.

What you seeWhat it points toWhat to do
"We couldn't verify your request. Please wait a moment and try again."The server rejected the request as invalid (HTTP 400). It is the only message that says "verify", so it may relate to the site's security check, though we can't confirm that from the outside.Wait a minute and retry. Reload the page and complete any "are you human" check yourself. Try turning off a VPN if you use one.
"Your session has timed out. Please start again."Your session expired (HTTP 401), usually from leaving the page open too long.Start again, with your passport, flight and hotel details open beforehand.
"The system is busy right now. Please try again in a moment."A server fault on their side (HTTP 500). Your entries are probably not the problem.Try later. Changing browsers won't help a server fault.
"The requested resource could not be found."A missing page (HTTP 404), often from an old link or a bookmark partway through the form.Go back to the site's home page and start from "Arrival Card".
"An error has occurred. Please try again."The catch-all for anything else.Retry once, then try a different browser or device.

When the page itself is the problem

A security check that keeps looping. The site sits behind a browser check. VPNs, strict privacy extensions and shared office networks can all make it harder to pass. Complete it by hand, and try a normal window with your phone's data connection if it keeps coming back. Don't use a tool that claims to skip it.

A button that does nothing. The form checks each field when you leave it, so a rejected value may be why Continue doesn't move on. Scroll up and look for a field marked in red. The field rules list what each one accepts.

Freezing on the accommodation step. Travellers report this one often, so it has its own guide.

Slow at busy times. Pattaya Mail warned before launch that systems like this can slow down under heavy traffic. If it crawls, come back at a quieter hour instead of pressing Submit repeatedly.

If you run out of time

The Royal Thai Embassy says submission is mandatory before arrival but can be completed until you reach immigration. Some airports offer WiFi for this, and it lists kiosks at Suvarnabhumi (BKK), Don Mueang (DMK), Phuket (HKT), Chiang Mai (CNX) and Hat Yai (HDY). Expect this to take longer than doing it beforehand. If you've got no other way, ask the staff there.

What not to do: don't search for a "TDAC help" service and pay it. The official route is free, and many of the top search results and ads are from other parties.

Questions people ask

Which browser works best for the TDAC?

We have no official answer. Forum reports mention more success on laptops and desktop browsers than on phones, but others filed fine on Android. If one fails, trying another is cheap.

Is the TDAC site down right now?

We don't monitor it, so we can't say. If you get the "system is busy" message on two different devices and networks, the fault is probably on the site's side.

Do I lose what I typed if the session times out?

Plan on it. The message says to start again, so keep your details in front of you.

A timed-out session is painful because you retype everything. ArrivalFiller holds your answers in your browser, so starting again is one press and a check.

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Where this comes from

Rules change, so check the official site before you travel. Where we quote a form's message, we copied it from the form's own public code. Some messages may rarely appear, and we don't run test submissions on government forms.