What documents are needed for applying for a DTV visa for my son as a dependent?

Seems you didn't provide a sponsorship letter for your dependant, along with financial proof.

So do exactly as they ask for, and upload the documents. You should be fine

..

I used chatgpt to help me write a sponsor letter when i did mine. Include your name, passport number, dtv visa number, your son's name, his passport number, that he is your biological son and state that you will be financially responsible for his food, accomodation and spending whilst in Thailand. Upload in a pdf file along with a copy of your passport (sign the copy with a pen).

In my experience, embassies don't usually accept digital signatures, so I've always printed everything, sign with blue ink and scan it before submitting

5-23 - do better next time.

You have to submit a cover letter mentioning that he is your dependent and you will sponsor him during his stay in Thailand.

Try to upload Cover letter, typed and signed by a family member who sponsors the trip, and whose name on the above bank statement along with a signed photocopy of passport of the sponsor (that's you)

Yes, ok. And your question is? :)