DIAGNOSIS This is almost always a Wi-Fi band mismatch. The C200 only works on 2.4 GHz networks, and if your phone is on your router's 5 GHz band during setup, it can't handshake properly.
FIX First, go into your phone's Wi-Fi settings and manually connect it to your 2.4 GHz network. Then, open the Tapo app and start the setup process again. Make sure you're entering the password for that 2.4 GHz network exactly, and keep the camera within 10 feet of the router for this initial pairing.
IF THAT DIDN'T WORK Some modern routers combine bands into a single network name. You might need to temporarily log into your router's admin page and split the 2.4 GHz and 5 GHz networks into two separate SSIDs with different names, just for the camera setup. You can usually combine them again afterward.
HEADS UP During setup, the camera creates its own temporary hotspot for your phone to connect to. If you get a prompt about "internet may not be available," tap to connect anyway. It's a normal part of the process.