@Agustin **********
I'm sorry, but that's not correct.
The standard government DTV flyer spells it out.
No matter on what basis you apply for the DTV, there is no requirement to prove income. You definitely need to prove that you already have enough money to fund yourself. Apart from that, you also need to prove that you are engaged in remote work, or required to be in Thailand for a specific purpose, such as education, sport training, medical treatment, etc.
They basically want you to justify that you are busy with something other than working in Thailand and that you're self-sufficient.