DIAGNOSIS Your source device is sending an audio format the soundbar doesn't understand in its current configuration. This often happens with high-bitrate formats like Dolby TrueHD from a Blu-ray player or specific PCM settings from a game console.
FIX The fix is on the source device side. 1) For your Apple TV, go to Settings > Video and Audio > Audio Format. Change it from 'Auto' to 'Dolby Digital 5.1'. This is a universally compatible format. 2) For a PS5, go to Settings > Sound > Audio Output. Set 'HDMI Device Type' to 'AV Amplifier', 'Number of Channels' to '5.1 ch', and 'Audio Format (Priority)' to 'Dolby Digital'. 3) Make sure the device is plugged into the soundbar's HDMI IN port, not the TV.
IF THAT DIDN'T WORK If you're using the TV's HDMI ARC port to send audio back to the soundbar, your TV might be the bottleneck. Go into your TV's external speaker audio settings and change the 'Digital Audio Out' format from 'Auto' or 'Bitstream' to 'PCM'. This forces the TV to decode the audio first, which the soundbar will always accept.
HEADS UP The 'unsupported audio' message will always show briefly when you first start a new format—that's normal. It's only a problem if it stays on the screen and you get no sound. The A7000 supports almost all common formats, but the chain of devices (player > TV > soundbar) has to be set up correctly for them to pass through.