What must I do - is it expiation or spending the money I swore to spend - after I broke an oath that I made binding by pledging to pay a sum of money in the event of breaking it?

If the swearer breaks his oath, he must offer expiation for the oath (kaffarat al-yameen), which is feeding ten poor persons, or clothing them, or freeing a slave. If he cannot find any of these, then he must fast for three days.

If what he committed to was a "nadhir al-lajaj" (an oath made in anger or to prevent oneself from doing something), then he is obligated to spend the amount he committed to spending, or offer another expiation for an oath. He has the choice between fulfilling what he committed to and offering the expiation for an oath.