The AO visa doesn’t need Board of Investment endorsement (that I’m aware of from any overseas embassy but please link details if you find that’s your case).
Getting a local GP to sign off on the medical part can be hard as they don’t generally do the specific tests required. Have a chat to a local (to Thailand GP) here.
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They’ll do a Skype type interview and confirm you don’t have elephantiasis or Syphilis and issue a certificate 😀