You cannot use cast iron cookware on an induction cooktop for two reasons. First, your cookware has to be compatible with the magnets within the cooktop for heat to be applied to your pan. For this reason, many induction cooktops come with a compatible pot or pan, or owners go out and buy a set for themselves. Second, the smooth top of an induction cooktop is quite fragile and will scratch if you use cast iron on it. To preserve the stylish surface, it's best to use soft cookware, not use harsh or abrasive cleaners, and avoid dragging your cookware of the cooktop as much as possible.