Diagnosis
The monitor is not handshaking with the camera. This is a pairing failure. It is most common after a power outage or when using a third-party power adapter.
How to Fix It
First, power cycle both units. Unplug the camera and monitor for 60 seconds. Use only the original eufy power adapters and cables. Plug the camera in first. Wait for its status light to turn solid green. Then plug in the monitor. It should pair automatically. If not, you must force a manual re-pair. Press and hold the power button on the camera for 10 seconds until you hear a beep and the light flashes blue. On the monitor, press the menu button, select 'Camera Settings', then 'Pair Camera'.
If That Didn't Work
The internal battery in the monitor may be fully depleted. Leave the monitor plugged into its charger, turned off, for a full 8 hours. This deep-charges the battery. Then attempt the pairing process again.
Heads Up
The monitor and camera communicate on a 2.4GHz FHSS signal. Wireless interference from a new router, microwave, or dense apartment building can cause this. Try moving the camera to a different power outlet, away from other electronics.