ANSWER:

If it’s a normal illness that he would recover from eventually then it’s not permissible to pay fidya. He must make up those days when he is cured. But if it’s a chronic illness then he should give the fidya.

My father is sick and will likely not be able to make up fasts. How to give food instead, does it have to be 1and half kilograms, do we give a one-time meal or groceries?