My Immigration has recommended changing the O-A visa to an O visa for which no proof of health insurance is required: Departure from Cambodia and return, inform at the border that you will apply for a retired O-Visa and either present only the 30-day certificate to the official or apply for a 60-day visa. Then take care of the rest in the immigration of the province (annual visa Non-Immigrant O). However, unfortunately, at the moment one has to wait for the borders to open again in both directions.