the index bin should appear from the right outlet of [fftin~]
you could use the [count~] object instead.
Could you show the whole pfft~ patch so it is easier to find a solution?
i see you connect the fftin~ outlet of the bin index, first to a [number~]. i think that the [number~] when used at the "~" state, does not send out the received values, so there migt be your problem. bypass it and see if it works!