See this from the FAQ page:
How do I use 2-way audio?
2-way audio allows users to listen and talk through the WyzeCam. It works like a walkie-talkie so you can speak or listen but you can’t do both at the same time.
Tap into the live stream feed view of an individual camera to use the 2-way audio feature.
To talk through the camera: Hold down the Voice icon. The camera will automatically turn on the sound to listen for a response when you release the Voice icon.
To listen through the camera: Tap the Sound icon to turn on sound for your live stream.
To use 2-way audio, the Wyze App must be able to access the microphone on your phone.
On iOS: go to your phone’s Settings. Tap Wyze. Turn on the toggle for Microphone.
On Android, go to your phone’s Settings. Tap Apps. Tap Wyze. Tap Permissions in the App Settings section. Turn on the toggle for Microphone