I'm trying to receive indicate via BLE connection, but I can't receive any data

I am creating an app for BLE connection for iOS. I can connect to the peripheral from central (iPhone6: iOS12.4.9) and send commands with I am able to send commands with writevalue.

https://developer.apple.com/documentation/corebluetooth/cbperipheral/1518949-setnotifyvalue

In the above setNotifyValue, there is a description that seems to be accepted by indicate. The following methods of didUpdateValueFor do not return.

Code Block 
func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) 

https://developer.apple.com/documentation/corebluetooth/cbperipheraldelegate/1518708-peripheral
If you know how to implement receiving data in indicate, please let me know.

Code Block 
func peripheral(_ peripheral: CBPeripheral, didUpdateNotificationStateFor characteristic: CBCharacteristic, error: Error?) 

(log)
didUpdateNotificationStateFor

<CBCharacteristic: 0x2833cde60, UUID = ***2000-XXXX-XXXX-XXXX-XXXXXXXXX, properties = 0x20, value = (null), notifying = YES>
************************

The sample code is shown below. I'm still working on it, so there may be some garbage code, sorry.