It is reasonable for a country to require visitors to buy insurance to cover medical expenses that may be incurred during the visit to the country.
The country should arrange the insurance with a local insurance provider for the mandatory coverage.
This type of insurance is necessary as the visitor may need hospital treatment for covid infection, which is now quite common, and may affect more than 1% of visitors.
The visitor can pay for the compulsory insurance at the point of entry and treat it as part of the cost of travel to that country. After all, they have to pay visa fee (in some cases) and the airline and hotel bills.
Tan Kin Lian