Is it permissible to pay expiation for the days I missed fasting in previous Ramadans due to a legitimate reason, without making them up, knowing that I suffer from extreme emaciation (my height is 165 cm and my weight is 38 kg) and low blood pressure, and I work long hours, and I fast Ramadan with extreme difficulty?

The days missed in Ramadan must be made up (qada'), along with an expiation (kaffarah) for delaying the make-up, if the person was capable and aware of the ruling concerning the delay. Otherwise, no expiation is necessary. If a trustworthy doctor states that one is permanently unable to fast, then it is sufficient to feed one poor person for each day (approximately 750 grams of the staple food of the country). The basic principle is that making up the fasts gradually is obligatory as long as one is capable.