Medical certificate: It depends for which country a client requires the oxygen if the provision of a medical certificate is an obligation. If we do not require a medical certificate with the enquiry it could be that it is not needed at that stage. In case of a regular referrer we often do not require the medical certificate in certain countries at the day of the enquiry but obligate the referrer to be able to supply the medical certificate within 24 hours if, at some stage, needed.