By default, when an iOS device receives an incoming call, the device will display the call screen. Unfortunately, this will cause the Switcher Studio app to close, even if you're broadcasting or recording. In order to prevent incoming calls from closing Switcher, we highly recommend using the Do Not Disturb (DND) feature on all your devices.
Turning on Do Not Disturb
Open the Settings app on your device.
Tap Do Not Disturb to open the DND preferences.
Switch your phone to Do Not Disturb mode to disable incoming calls and texts.
Set Allow Calls From to No One.
Set Repeated Calls to Off.
Set the Silence preference to Always.
Switch your phone to Airplane Mode.
Open your WiFi settings and turn it back On.
Connect to the desired network.
Your Do Not Disturb menu should resemble this screen-capture: