When you're using the Music App, you can choose the "AirPlay icon" -  or you can select the system-wide audio settings, then select sound and tap the AirPlay icon. We recommend you to choose the AirPlay from your Music App that lets you use the latest AirPlay protocol. While starting from the system-wide audio settings, it'll output every sound on your system to WiiM Mini (including your notification sound) and uses legacy AirPlay protocol.