- KKBOX developed an Apple Watch app to allow users to control music playback from their watch, view lyrics and playlists, and listen to radio stations. - During development and testing at Apple's Watch Lab, they encountered several challenges not present in the simulator, including app crashing on launch, slow loading of images and tables, and issues with communication between the watch and phone. - Through testing on real devices, tweaking the communication methods, caching images, and focusing on the core playback functionality, KKBOX was able to solve the problems and ship a stable music experience on the Apple Watch.