Your ROOT_URL in app.ini is https://source.parasitstudio.de:63000/ but you are visiting https://source.parasitstudio.de/wirtz/OpenAudio_ArduinoLibrary/src/commit/624f14283e781404171c7952ecf7e390266c1d60/examples/MixStereoToMono_Float
You should set ROOT_URL correctly, otherwise the web may not work correctly.