iOS validate paid app receipt

I'm trying to move my paid app to in-app purchase. First of all I had to validate if app was already purchased. I implemented receipt validation with following code:

func validatercpt() {
    let receiptURL = NSBundle.mainBundle().appStoreReceiptURL
    if NSFileManager.defaultManager().fileExistsAtPath(receiptURL!.path!) {
        print("OK")
    }
    else {
        print("refresh")
        let refreshReceiptRequest = SKReceiptRefreshRequest()
        refreshReceiptRequest.delegate = self
        refreshReceiptRequest.start()

    }
}

the receiptURL does not exists so I try to refresh the receipt.

func requestDidFinish(request: SKRequest) {
    print("req finish")
    let receiptURL = NSBundle.mainBundle().appStoreReceiptURL
    if NSFileManager.defaultManager().fileExistsAtPath(receiptURL!.path!) {
        print("OK")
    }
    else {
        print("not exists")
    }
}

Even after refresh, the receipt still not exists.

Any suggestions?

Thanks, Max