People show absolute dedication by fasting for long thirty days without water during the month of Ramazan. But sometimes out of your least expectations, it happens that you’re unable to fast. I understand. There may be health issues, your old age and even genuine reasons like pregnancy. The people suffering from any of these can be exempted from fasting but only on specific rules and regulations.
Apart from the zakat that we offer to the needy and underprivileged, fidya is the charity that is made to compensate your non-fasting days. It is necessary to offer one meal to a person in a day if you’re not fasting during the month, but giving charity is just an alternative for that.

The only difference between a fidya and karrafan is that fidya is intentional charity during or before the month (you’re aware that you won’t be able o fast), while karrafan is the unintentional charity made to keep abiding to the protocols of Ramazan. The karrafan is supposed to be equal to the meal of sixty people’s single meals instead of one.
By this the people who are in need get a meal and charity, which is one of the purest things about Ramazan, sacrificing!
There are various applications on google play too that are only charity based made for Ramazan.