Your ROOT_URL in app.ini is https://source.parasitstudio.de:63000/ but you are visiting https://source.parasitstudio.de/wirtz/esp-link/src/commit/bee59297518278afb040dc46e1e9eb411027ab45/arduino/libraries/EspLink/examples/EspLinkWebApp/web-page You should set ROOT_URL correctly, otherwise the web may not work correctly.