You would think it’s straight forward but some people get rejected for no reason, even though they seem to have all necessary documentation. They have been told, a stamp is missing on a work certificate even though the requirements published on the embassy website do not state the necessity. Or some have been issued tourist visas instead of DTVs. Search this group for all these stories. Some cases are complicated. Passport from country A, bank account in country B, application in country C. If an agent “guarantees” the visa, you know where part of the “fee” goes to.
I tried with seaman’s book and ship contract, it’s not acceptable, because you work outside of the country and not remotely IN Thailand. If you are a seaman and got approved, please share the embassy and documentation provided.