The article below may be able to help you with this issue.
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I've quoted some helpful highlights for you:
You can AirPlay videos, music, or photos from a variety of different locations on your iOS device, including from within the Photos, Videos, Safari, and Music apps, or directly from recently used apps.
To AirPlay video or photo content to your Apple TV:
- Connect your iOS device and Apple TV to the same Wi-Fi network.
- Open either the Videos, Safari or Photos app on your device.
- Locate and tap the AirPlay icon (if attempting to AirPlay video content from Safari or Videos, begin playback first).
- Select your Apple TV from the list of available devices that appears and begin playback.
To AirPlay audio content to your Apple TV or AirPlay speakers or receivers, including AirPort Express:
- Connect your iOS device and Apple TV, AirPlay speakers, receiver or AirPort Express to the same Wi-Fi network.
- Open the Music or Safari app on your device.
- Locate and tap the AirPlay icon.
- Select your Apple TV, AirPort Express, or AirPlay-enabled speakers or receivers from the list of available devices that appears, and begin playback.
Note: The images of a TV screen or speaker next to each AirPlay device in the AirPlay menu indicate the type of media content you can stream to that device.
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