The Custom DNS option allows you to control the default DNS server settings of your Air SIM devices. However, if your device also has its own custom DNS server settings, they will typically have priority above the Custom DNS settings specified in the User Console.
If your device is not using your Custom DNS settings as you expected, please check the network settings in your device to ensure that there are no other settings overriding the Air SIM Custom DNS settings.
Please note: if your device has an active session, it will continue to use existing DNS settings. You will need to disconnect the session by rebooting the device, disabling and re-enabling the Air SIM network adapter, or other method. Once the device reconnects and creates a new session, it will receive the Custom DNS settings.