Your ROOT_URL in app.ini is https://source.parasitstudio.de:63000/ but you are visiting https://source.parasitstudio.de/wirtz/OpenTheremin_V3_with_MIDI/src/commit/63ab93c47da662e32870f6bd1bf21bbeb6bdd246/Open_Theremin_V3 You should set ROOT_URL correctly, otherwise the web may not work correctly.