They will contact your UK GP, and access your records, before issuing a policy, most will not cover you. If they do issue a Policy they will give you a policy that only covers Covid and Accident and Emergency for a premium.
The Invoice must have your Full Name andThai address on it, otherwise they will not accept it, I was given one from the True Shop, with just my name on, had to trudge back and join the queue again, to get the right invoice.