Is it permissible to pay monetary expiation instead of making up nearly two months of Ramadan fasting due to unknowingly breaking the fast and the current difficulty of fasting because of smoking?

You must make up for the missed fasts, along with seeking forgiveness and repentance. It is not permissible for you to feed the poor as an alternative as long as you are capable of fasting. You must also rid yourself of the habit of smoking.