JY-UOS03N4G Volume Problem
I bought the JY-UOS03N4G head unit on https://www.joyingauto.eu.
connected head unit, switched on smoothly, Functions are working,  Sound is on.
However, when I want to turn up/down the volume the sound does not increase/decrease,  the volume remains constant.
Only at level 0 the sound is muted completely.
The volume level cannot be adjusted.
Is there a setting or something I'm missing?

Volume is not controlled.
The level on screen is increasing/decreasing (13->14->15 or 15->14->13) but the actual volume stays the same.

Links for About section images:
About Device (1/3)
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