The ARC function on a TV allows it to send audio and control commands to a connected audio product. This allows the TV to switch on the audio product when needed, and also to control the volume from the TV remote.
No signal shown on the front panel or no audio output from your connected product
Make sure the HDMI input on your TV supports ARC
Make sure the TV is set to use a connected audio system rather than its internal speakers
Make sure that the audio output of your TV is set to 'Stereo PCM (Uncompressed)'
Make sure your HDMI cable is compatible with HDMI 1.4 or above
TV will not switch on or control your connected product
Make sure that 'TV Power Control' is enabled in the StreamMagic app on the ARC source settings page