Can I enter Thailand with an expired DTV visa and no return ticket?

Departure date is optional. Leave it empty.

You just need proof of onward travel with 180 days.

If your Visa was valid to November 2019............................. I think you might be refused entry.

Buy a onward ticket. €14

A flight ticket that expires after 72 hours is usually a temporary flight reservation (also known as an option or onward ticket). You often use this as proof of an outbound flight for a visa application. After 72 hours, the reservation expires automatically and is cancelled without you having to pay for the entire ticket.

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As already written here, you should check upfront which information is mandatory and which one is optional that would save you time and effort.

As you may know the DTV doesn't grant you access to the kingdom. Even though it is unlikely the immigration officer can deny entry if you are not able to provide an outbound ticket within the permitted stay of 180 days. Also, as already mentioned here, your airline could ask for it at check in.

Lastly, please note that Thai embassies are part of the Ministry of Foreign Affairs. However, the Arrival Card is issued by Thai Immigration, which is under a different authority. This means that, from an organizational standpoint, the embassies have nothing to do with the TDAC, and for that reason alone, they may not be able/don't want to answer such questions.

You only need to fill in the asterisk highlighted * fields in the TDAC form these are mandated everything else ignore. As Graham has already mentioned you need to check with your airline if you need an onward or return ticket. I know when i flew with thai airways from singapore to bangkok the check in lady was abiut to ask if I had a flight out of thailand until I showed her my DTV at that point she said I didnt need to show anything and checked me in !!!

Ask your airline if they require a departure ticket if you enter with a DTV as this is where you might get asked

Departure information is not mandatory. Leave it blank. Indeed don’t even click in one of the boxes otherwise it becomes mandatory.