IOS-DFU-Library: Error 304: Enabling notifications failed

When I’m trying to Firmware updation , it’s not working, here is log =

<CBPeripheral: 0x1740f5a00, identifier = 907980BC-8FC6-4675-8A2A-F2EFAB1A16EC, name = SIDEKICK, state = connected> Changed state to: Connecting I : Connected to SIDEKICK I : Services discovered V : Starting Secure DFU… I : Connected to SIDEKICK I : Services discovered V : Secure DFU Service found V : Discovering characteristics in DFU Service… D : peripheral.discoverCharacteristics(nil, for: FE59) I : DFU characteristics discovered V : Enabling notifications for 8E400001-F315-4F60-9FB8-838830DAEA50… D : peripheral.setNotifyValue(true, for: 8E400001-F315-4F60-9FB8-838830DAEA50) Changed state to: Starting E : Enabling notifications failed E : Error 3: Writing is not permitted. V : Disconnecting… D : centralManager.cancelPeripheralConnection(peripheral) D : [Callback] Central Manager did disconnect peripheral I : Disconnected Error 304: Enabling notifications failed

Please let me Know what was the issue

func startDFUProcess() {
        guard dfuPeripheral != nil else {
            print("No DFU peripheral was set")
            return
        }
```
        
        let dfuInitiator:DFUServiceInitiator = DFUServiceInitiator(centralManager: appDel.manager, target: dfuPeripheral!).with(firmware: selectedFirmware!)
        dfuInitiator.delegate = self
        dfuInitiator.progressDelegate = self
        dfuInitiator.logger = self
        
       dfuInitiator.enableUnsafeExperimentalButtonlessServiceInSecureDfu = true
        
        dfuController = dfuInitiator.start()
    }`