Am I obliged to offer an expiation for delaying the making up of past Ramadan fasts, knowing that I was unaware of its obligation until the day I intended to make up the remaining days I owed?

The fidyah is obligatory for anyone who delays making up missed fasts until the following Ramadan without a valid excuse or ignorance, and it involves feeding one needy person for each day. However, for those who make up the missed days before the beginning of the next Ramadan, there is no fidyah upon them, because the time for making up the fasts is extended until the next Ramadan, and hastening to do so is commendable.