Low volume when casting from spotify app

[Roy35]

Plan

Premium

Country

netherlands

Device

Iphone 12

Operating System

IOS14.4.2

My Question or Issue

I still have this problem of low volume when casting spotify to smartspaker after the following actions:

- clean reinstall of the spotify

- factory reset of the Harman Kardon

- reset of routers

casting device; iphone 12

Version of spotify app: 8.6.12.1032

firmwareversion of google cast: 1.40.168834

see also: https://community.spotify.com/t5/Ongoing-Issues/Low-volume-casting-with-Chromecast-Audio/idi-p/48900...

it is really annoying, very low volume when casting spotify so you have to double the volume of your system. If somebody then turns on the television the windows almost blow out

Already tried casting with Deezer and that works perfect. I dont really want to change over to Deezer but Spotify keeps failing to solve this issue.