"callback must be a function" issue with Node.js/Express

my openstates.billDetail function has a call back function inside of it, and I'm getting an error: 'callback must be a function', but my callback appears to be a function!

app.get('/search/:searchTerm', function(req, response) {
    var nameArray = req.params.searchTerm.split('_');
    var bills = []
    var billIds = []
    openstates.legSearch({
        first_name: nameArray[0],
        last_name: nameArray[1]
    }, function(err, data) {
        if (!err) {
            openstates.billSearch({
                state: 'CA',
                chamber: 'lower',
                page: '1'
            }, function(err, data) {
                for (var billIndex = 0; billIndex < data.length; billIndex++) {
                    billIds.push(data[billIndex].id)
                }
                for (var billIdIndex = 0; billIdIndex < billIds.length; billIdIndex++) {
                    openstates.billDetail(billIds[billIdIndex], function(err, data) {
                        console.log(data);
                    })
                }
            })
        }
    })
})

Anyone have any thoughts on this? my other callbacks work fine...