Within the video session, the microphone and camera icons in the bottom bar must not be crossed out but must be as shown in the image below:
Check that the camera and microphone are not physically blocked.. If you are using a headset, make sure you have not muted the microphone using the headset button.
Make sure you have a sufficient WiFi or mobile data connection
To make the video session work, check that the Wi-Fi or mobile data icon has at least one bar. If not, try moving or changing networks.
Restart the app or your device
Try closing and restarting the app. Alternatively, restart your device.
Make sure your device's battery is sufficiently charged
Check that your device’s battery is sufficiently charged. If not, charge it.