Install the app on the Android TV/Fire TV (server) and on the mobile/tablet that sends the notifications (client).
First start the app on the Android TV / Fire TV. An overview with the IP address should now be displayed.
After starting the app on the mobile phone you will see possible devices. If the device is in the list, select it and continue. Otherwise you can enter the IP address manually. Please note that the IP address of the Android TV/Fire TV should not change, otherwise you have to do the setup again. With many routers, you can assign a fixed IP address. Otherwise, you can also assign a static IP address on the Android TV/Fire TV.