Thx for reply thaiscot.
Below is what the London Embassy demand. Accumulating all that documentation is just too time consuming.
Non-Immigrant Type O- A (Long Stay) 1 Year/Multiple entries
Printout of visa application form submitted online, with bar code
Passport or travel document with validity not less than 6 months and at least 2 blank pages
A medical certificate issued in the UK or Ireland or Thailand, showing no prohibitive diseases as indicated in the Ministerial Regulation No.14 (B.E. 2535) which include Leprosy, Tuberculosis, Elephantiasis, drug addiction, third stage of Syphilis, and the certificate shall be valid for not more than three months.
Certificate of criminal record clearance from the UK (ACRO, DBS, or issued by the police) or Ireland
Financial evidence showing monthly income of not less than 65,000 THB (approx. £1,625) or having the current balance of 800,000 THB (approx. £20,000), e.g. bank statements, proof of earnings, for at least 1 month
Copy of evidence stating that applicants have insurance as per stipulated by the Office of Insurance Commission and health insurance of Thailand which covers COVID-19 related medical expenses, both inpatient and outpatient, no less than 100,000 USD for the whole period of your stay in Thailand.
Please check < http://longstay.tgia.org> for more information regarding the insurance requirement.