On macOS, media buttons are supposed to work out of the box. If this is not the case, go to macOS Settings > Privacy & Security > Accessibility and you will find Crates there. Turn on the toggle and restart Crates (Quit via menu or CMD+Q & launch again). If it’s not working again, go to Accessibility Settings, remove Crates using the – on the left bottom side of the panel and either add it manually (and flip the switch on) or restart Crates and it should be added again. For good measure, restart the Crates UI completely every time you make some change to this setting.