CXPlayDTMFCallAction doesn't play local dtmf sound

I am integrating CallKit with VOIP app. I was able to make incoming and outgoing calls. I followed the step:

1. ConfigureAudioSession
2. startAudio in (didActivate)
3. stopAudio in (didDeActivate)

I have implemented the callbacks for DTMF provider delegate as shown below:

func provider(_ provider: CXProvider, perform action: CXPlayDTMFCallAction) {
    print("Provider - CXPlayDTMFCallAction")

    let dtmfDigts:String = action.digits

    for (index, _) in dtmfDigts.characters.enumerated() {
        let dtmfDigit = dtmfDigts.utf8CString[index]
        print("Processing dtmfDigit:\(dtmfDigit)" )
        self.softphone.dtmf(on:dtmfDigit)
    }

    self.softphone.dtmfOff()

    // Signal to the system that the action has been successfully performed.
    action.fulfill()
}

I don't hear key-press sound i.e., local dtmf sounds when I press a number on the native in-call UI during the call.

From https://developer.apple.com/reference/callkit/cxplaydtmfcallaction:

"CallKit automatically plays the corresponding DTMF frequencies for any digits transmitted over a call. The app is responsible for managing the timing and handling of digits as part of fulfilling the action."

Is this a known issue or callkit doesn't play the local dtmf key press sounds?

I was able to make it work by:

func provider(_ provider: CXProvider, perform action: CXPlayDTMFCallAction) {
    print("Provider - CXPlayDTMFCallAction")

    self.softphone.audioController.configureAudioSession()

    let dtmfDigts:String = action.digits

    for (index, _) in dtmfDigts.characters.enumerated() {
        let dtmfDigit = dtmfDigts.utf8CString[index]
        print("Processing dtmfDigit:\(dtmfDigit)" )
        self.softphone.dtmf(on:dtmfDigit)
    }

    self.softphone.dtmfOff()

    // Signal to the system that the action has been successfully performed.
    action.fulfill()
}

Note: I added self.softphone.audioController.configureAudioSession().

-(void) configureAudioSession
{
    // Configure the audio session
    AVAudioSession *sessionInstance = [AVAudioSession sharedInstance];

    // we are going to play and record so we pick that category
    NSError *error = nil;
    [sessionInstance setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];
    if (error) {
        NSLog(@"error setting audio category %@",error);
    }

    // set the mode to voice chat
    [sessionInstance setMode:AVAudioSessionModeVoiceChat error:&error];
    if (error) {
        NSLog(@"error setting audio mode %@",error);
    }

    NSLog(@"setupAudioSession");

    return;
}