FACTORY RESET THE CAMERA.
Reset the camera by pressing the reset button on the back of the camera for 20-30 seconds. The manuals say "10 seconds" but mine didn't successfully reset after 15 seconds, so I eventually just held for 30 seconds and that worked. You'll know it works because the red LED lights (on mine, anyways) flashed once, then the device reboot. If the green light starts blinking, it failed - try again.
GET THE IP OF THE CAMERA
I got mine by logging into my router and looking at all the client list.
LOGIN TO THE ADMIN UI
Go to http://192.168.1.99/adm/enable_ui.cgi (replace 192.168.1.99 with your camera IP) -- Most comments say going to http://192.168.1.99/ they could login -- that gave me a 404. Go to http://192.168.1.99/adm/enable_ui.cgi and login with username "administrator" and empty password. IF the login doesn't work, then your device wasn't successfully reset in step 1, start over.
Thanks to all whose comments helped! 🙂