My second camera in my 2 pack would not connect. I tried for over two hours. I looked to community but didn't find a complete solution. I finally uninstalled the Google Home App. I performed a factory reset on the two wireless cameras by pressing the button on the back of the camera head for five seconds. I installed the Google Home App again. I, first did a set up on the SECOND wireless camera, which I could NOT get connected. It finally connected. I set up the FIRST camera which initially DID connect, it now also connected. I have both cameras connected.
It looks like you encountered the same problem that a lot of customers with existing Google Nest devices are having trouble installing additional Google Nest cameras or doorbells or other devices. It seems that the install process attempts to communicate with an already-configured Nest device to obtain the SSID and password for your network--apparently to save you time. However, something goes wrong and the customer gets a "cannot communicate with assisting device" error or a failure to connect error. We have been lucky this hasn't happened to us, but lots of other customers have, as in this very long thread:
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