sumQuantity in HKStatisticsCollectionQuery returns nil when fetching step count on hourly basis

I want to fetch step count from Health app on hourly basis.

But statistics.sumQuantity() in below code always returns nil value.

Note : As I want step count on hourly basis within same day so I am passing startDate and endDate both are same.

In below code output is always, No Step quantity.

let predicate = HKQuery.predicateForSamples(withStart: startDate, end: endDate, options:[ .strictStartDate])
    
var interval = DateComponents()
interval.hour = 1

let query = HKStatisticsCollectionQuery(quantityType: sampleType,
                                        quantitySamplePredicate: predicate,
                                        options: [.cumulativeSum],
                                        anchorDate: startDate,
                                        intervalComponents: interval)

query.initialResultsHandler = { query, statsCollection, error in
    if error != nil {
        completion(nil, error)
        return
    }

    var totalSum = 0.0
    if let myResults = statsCollection { myResults.enumerateStatistics(from: startDate, to: startDate) { statistics, stop in

            if let quantity = statistics.sumQuantity() {
                let date = statistics.startDate
                let steps = quantity.doubleValue(for: HKUnit.count()) 
                totalSum = totalSum + steps
            } else {
                print("No step quantity")
                let steps = 0.0
                let date = statistics.startDate
            }
        }
    }
    
    DispatchQueue.main.async {

    }
}
self.healthStore.execute(query)