What is the expiation for not making up menstrual fasts over years, despite having the means and being unable to fast?

You must make up for all the days you missed in previous Ramadans to absolve yourself. You are obligated to pay an expiation (kaffarah) for every day you did not make up without a valid excuse until the next Ramadan began, provided you were aware of the impermissibility of the delay. However, if you were unaware of the impermissibility of the delay, then you are only required to make up the days without expiation, as some jurists have stated. The Hanafis do not obligate a fidyah at all for delaying the make-up days.