Diagnosis
The parent unit needs to be manually paired with the new camera. Out of the box, it's only looking for its original paired camera.
How to Fix It
Here's the pairing process: 1. Turn the parent unit OFF. 2. Plug the NEW camera into power and wait for its light to be solid (not blinking). 3. Turn the parent unit ON while holding down its "Menu" button. Keep holding until you see the wireless icon or a channel indicator appear. 4. It should now search and connect to the new camera. You may need to repeat this to switch back to your original camera.
If That Didn't Work
Ensure the cameras aren't both plugged in and powered on at the same time during this process. Having the original camera powered on can confuse the pairing. Unplug the original camera while pairing with the new one.
Heads Up
The HB6550 parent unit can only display one camera at a time. You're not setting up a split-screen view. You're teaching it which single camera to connect to. To switch between cameras, you'll need to repeat the pairing process each time, or get a second parent unit.