The night vision should stay on consistently when it is dark.
If the night vision is blinking in full darkness, that indicates a hardware or setup issue.
The most common issue is power. Often people will use a micro-USB cable attached to the provided power supply in order to extend the length. That causes issues because of the voltage loss.
I recommend checking the power to verify that the camera is connected directly to the provided power supply, which is then connected directly to the wall.