How can I book a sealed flight from London to Koh Samui that meets the Samui Sandbox requirements?

Regulations require that if Samui is your first destination in Thailand, your transit flight from Bangkok to Samui must be booked on the same through itinerary as your incoming international flight only on one of the special "Sealed Route" Bangkok Airways flight numbers which are always 4 digits beginning with "51".

The special designated "Sealed Route" flights are only for international arrivals, and are only bookable in conjunction with the international flight. This is to prevent mixing of international passengers (who have not yet had arrival covid tests) with the normal domestic passengers (who do not have such screening requirements) to prevent the risk of spreading Covid from the international travelers to domestic travelers.

The sealed route flights cannot be bought separately and can only be booked by your international airline carrier as part of your incoming single itinerary with your international flight. These special sealed route flights cannot be found for sale on the Bangkok Airways website, since they are not bookable by the public. If your flight number IS for sale on the Bangkok Airways website when you search flights, then it is a normal domestic flight and CANNOT be used for the sealed route. Any similar flight numbers do not count: for example, PG5171 is NOT the same as PG171 which also flies daily.

Book a combined ticket through Bangkok with a Bangkok Airways flight that starts with a 5. I believe there’s 3 a day. It must be one booking PNR.