Why does the Xiaomi Outdoor Camera BW500 whistle or have no sound during a voice call?

The Xiaomi Outdoor Camera BW500 has a built-in microphone, which enables two-way communication between the mobile phone and the camera.
If the device whistles or has no sound during a voice call, please refer to the following troubleshooting methods:
1. During a voice call, please try your best not to place the phone and the device in the same space, and stay away from the device for more than 10 meters. It is a normal phenomenon that the echo whistling is generated by the close calls;
2. If there is no sound during the call, please check whether the volume of the phone is adjusted too low and make sure that the Mi Home APP has obtained permission to use the phone’s microphone (recording).