What is the penalty if one vows an act other than fasting, like prayer, and becomes incapable?

Primary text

If one vows an act other than fasting, such as prayer, and becomes incapable, only the expiation of an oath is due, because the Sacred Law has not established a substitute payment for such acts. If the incapacity is temporary and expected to cease, the ruling is the same as that detailed for vowed fasting.