If the illness is chronic and there is no possibility of recovering from it, a person should feed one poor person for every day missed. Money can’t be paid directly to the poor as one must feed him and not give him money.
It is permissible to give food to one poor person all in one go but it must be given in food, not cash and its best to give the fidyah where you live.
Kindly refer to the following link(s):