When AirPlay is malfunctioning on Roku, first confirm that both your Roku and Apple devices are on the same Wi, Fi network. Next, ensure that AirPlay is turned on in the Roku settings (Settings > Apple AirPlay and HomeKit), and both your Roku OS and iOS/macOS are updated. After that, reboot your two devices as well as the router. In case the problem persists, perform a network settings reset on the Roku and also try turning off AirPlay and then turning it on again.