What was the cause of the Champaran movement?

Englishmen owned most of the arable land in the Champaran district of Bihar. They forced the tenants to grow 15% of their holdings with indigo as Blue dye was highly demanded in Europe. The entire harvest was to be given to the landlords as the rent. When Germany developed synthetic indigo, Englishmen sought to cancel the contract with the sharecroppers if they paid the amount of compensation. Some people agreed to this and gave money, but when they came to know of the real cause, they wanted their money back. This led to a tussle between the two and the series of events that followed  finally came to be known as the Champaran movement.