TV not reacting on UE48H series

I'm trying to use samsungctl for my Home Assistant. When using the application via command-line (e.g. samsungctl -vvv --host 192.168.*.* --port 8001 --method websocket KEY_MUTE) I get the output:

Access granted.
Sending control command: KEY_MUTE
Connection closed.

But nothing happens on TVs side.

Here's my http://<ip>:8001/api/v2/ output:

{
  "id": "07270e01-0078-1000-8cd0-84a466e9dad3",
  "name": "[TV]Samsung LED48",
  "version": "2.0.24",
  "device": {
    "type": "Samsung SmartTV",
    "duid": "07270e01-0078-1000-8cd0-84a466e9dad3",
    "model": "14_X14_BT",
    "modelName": "UE48H6400",
    "description": "Samsung TV RCR",
    "networkType": "wired",
    "ssid": "",
    "ip": "192.168.*.*",
    "firmwareVersion": "Unknown",
    "name": "[TV]Samsung LED48",
    "id": "07270e01-0078-1000-8cd0-84a466e9dad3",
    "udn": "07270e01-0078-1000-8cd0-84a466e9dad3",
    "resolution": "1920x1080",
    "countryCode": "DE",
    "msfVersion": "2.0.24",
    "smartHubAgreement": "true",
    "developerMode": "0",
    "developerIP": "0.0.0.0"
  },
  "type": "Samsung SmartTV",
  "uri": "http://192.168.*.*:8001/api/v2/"
}

Do I need to initiate or set something or is it maybe useful to factory-reset the device?
Thanks in advance.