The rates of the jizya varied from places and to places and were subject to local customs. The money so collected were, in theory, to be used for charitable purposes and salaries of salaries of the civil authorities. In practice they often ended up in the rulers' private coffer.
A convert to Islam was, in theory, no longer required to pay the jizya. Faced with increasing financial difficulties, however, the Umayyad caliphs demanded that the convert continues to pay the jizya. This discrimination, and the grief it caused, eventually led to a rebellion in 747 and the downfall of the Umayyads.