There is a bug in older releases of Konftel 300IP or Konftel 300IPx, which made it impossible to login in with newer versions of web browsers (Chrome, Edge, Firefox, etc.).


Try and log in with Internet Explorer or Firefox (version 52 or earlier, https://ftp.mozilla.org/pub/firefox/releases/52.0/win64/en-US/). After you have logged in successfully you can upgrade the software version to the latest and after that you should be able to login with any browser.