I have been having this exact problem with my Stick Up Battery Cam, and resolved it by disabling my Google Fi VPN. The hint for me was that it was working on my iPad via WiFi, but not on my Android phone either via WiFi or via Google Fi data service. And the camera was activated each time I clicked on Live View, and the spinning circle paused for a split second as if the app was about to receive a feed, but it never showed up even while my iPad did at the very same time.
Once I went into my Pixel’s Network and Settings/VPN page and disconnected from the Google Fi VPN, and clicked Live Feed exactly as before, the video appeared on my phone. I tried all sorts of other solutions and there is no doubt that this was my problem.
While this is likely not your exact issue if you’re on an iPhone or don’t use Google Fi, a VPN service may be blocking the video feed from the device. Good luck!