Hello all!
for Hanoi thai Embassy, I asked them about muy thai activity as for DTV application, they said, they need letter of acceptance and invoce that you paid and work permit of muy thai centre
TLDR : Answer Summary
To apply for a DTV visa related to Muay Thai at the Thai Embassy in Hanoi, applicants must provide a letter of acceptance from a Muay Thai center, an invoice confirming payment, and a work permit from the Muay Thai center.
DTV VISA RESOURCES / SERVICES