I am using the Deezer app music. It worked well, I could use the media buttons to control play/pause/next track/previous track. But a few days ago, (after an macOS update?) now when I hit play/pause it launches iTunes instead of controlling the Deezer app that is already running and playing music. It was correctly functioning before, so I don't know where this change of behaviour is coming from. This is very annoying as it makes the Deezer almost unusable as I have to bring it to front to control it.
Found the answer on the Deezer community forum:
You have to allow Deezer the accessibility rights, go to:
- System Preferences
- Security and Privacy
- Privacy tab
- Choose "Accessibility"
- Add "Deezer" to the allowed software
You'll have to unlock the configuration by clicking on the lock and enter your system password.
The original answer can be found here.