When I'm using the DRmare Spotify Music Converter and open it with the Spotify app, it also pops up an error message saying 'the application isn't installed'. I contact its support team and fix this issue well. It says I'm using the Spotify app for the Windows Store version and need to uninstall it and install the official version. I followed this suggestion and solved my problem well.
Although now it also works with the Windows Store version, I think you met the same situation because of the compatible issue. Do what I did to see whether your issue could be fixed well too.