What should I do if I need to provide a flight ticket for my DTV application but haven't purchased one yet?

Hi there! I applied for the DTV as Spanish citizen on December 30. On January 15 I got requested more documents. Today January 26 I was about to answer.

Some of the docs they request, like bank statements for last 3 months, I had already provided them initially to my application. Or "a concise overview of your professional activities during your stay in Thailand".

I already provided a cover letter explaining all (Remote Software Engineer).

I will upload same docs again.

BUT additionally, they request me the flight ticket to Thailand, which I didn't buy it yet because before purchasing any flight I wanted to have the DTV accepted. Only then spend more money in a flight.

WHAT should I do in this case? What do I attach? I ignore it? I attach a short letter telling that I will purchase the flight once my DTV is granted?

P.S. It's not even clear to me when I will move to Thailand. If I get the Visa granted, I plan to go before June, but in my application I put end of February. If they deny my DTV (though they shouldn't as I meet the requirements), I'm not buying a flight for the moment.