@John_A_S Hello,
If the Tapo camera is on 1080P, it will take around 300MB for one hour live streaming; The camera does not 'transmit video' while you are not watching live view.
App will consume data when it works in the background as camera would always be connected to the cloud server to make sure remote control is available all the time;
We haven’t tested the camera when it is just connected to the router without any live stream, and I am sorry that we do not have this data usage yet. You may purchase one and test it in your actual environment within return window
Besid, it is recommended to put camera in an open area where it could receive strong Wi-Fi signal from the router.