The correct answer to this open question is the following.
One reason for Martin Luther’s critique of the Catholic Church in the early 1500s was the fact that the Catholic Church was using indulgences for financial benefits, and Martin Luther heavily opposed to that action.
German monk Martin Luther started to have differences with the pope and the Catholic Church for many different reasons. The main reason was the belief that the Church could forgive sins by paying money. Indeed, in 1517, he wrote a book called "95 Theses," where he exposed some negative practices of the church and started the Protestantism movement that ended up with a division between protestants and Catholics.
