(6) Only for an alien, who has been granted Non-Immigrant "O-A" Visa, must have health insurance or non-Thai social
welfare covering medical expenses including the ones for Covid-19 disease with the coverage of no less than 100,000 USD or 3,000,000 baht for the entire duration of stay ni the
Kingdom.
(6.1) In case of purchasing Thai health insurance,
an alien can purchase through the website: longstay.tgia.org. (6.2) In case of purchasing foreign insurance or
having non-Thai social welfare,
foreign embassy in Thailand or a signature of authorized
person on submitted documents (Notary) must be certified
by the Ministry of Foreign Affairs of an applicant.
(6.3) In case an insurance company totally or partially
denies a health insurance's purchase, an alien must have a deposit in acommercial bank located in Thailand ofno less
than 3,000,000 baht at least
application or have a deposit in a commercial bank located in Thailand and other health insurances with total sum of no less than 3,000,000 baht for medical treatment and evidence
of denying health insurance's purchase certified by the said insurance company or a foreign embassy in Thailand or a signature of authorized person on submitted documents
(Notary) must be certified by the Ministry of Foreign Affairs of an applicant, depending on circumstances.
I would amend your excellent description to add that the insurance has to be from one of 14 Thai companies and that they are selective as to whom they insure.
I read here frequently people are denied and that is the reason cited. Surely it would be prudent to carry for multiple reasons as well as meeting all the other entry requirements?