Audio Mode only works when your mobile device is connected to the same Wi-Fi as the camera (indoor mode)
If your mobile device is connected to the same Wi-Fi as the camera but still shown as outdoor mode, please kindly reboot your Wi-Fi AP and see if the issue solved.
If the issue continues, please kindly check if you have open “AP Isolation” feature in your Wi-Fi router setting as AP Isolation feature would also block the camera to run in Indoor Mode.