No volume control with Bluetooth speakers

[eternia]

Hi,

My WiiM mini is connected over bluetooth to a set of speakers. When I connect to the speakers from my iPhone (over bluetooth), I have full volume control. However, when connected through the WiiM mini, the output is always at max. Fixed volume is off and I've also tried to limit the max volume, nothing works.
Any suggestions on how to limit the volume?

Best, Eelco