This is a softphone app for one of the largest VoIP providers in Germany. It is proprietary for this provider.
To further help you implement this, I attached my settings for the application, which I set up as a Custom App. When setup this way, it works for me. Also something to add, I renamed the setup file to setup.exe - I don't know if this is required though.
Turns out the regular Sipgate changelog also contains changelogs for the CLINQ application: https://www.sipgate.de/changelog