The Airbus Electronic Centralised Aircraft Monitoring (ECAM) system is great in making the pilot’s job a lot easier. Unfortunately, things might become confusing.
When the ECAM shows L/G GEAR NOT DOWN this indicates a sensor failure and you will not have the “3 greens” on the centre console (top row images). When you get the ECAM message L/G GEAR NOT DOWNLOCKED, you better go around and try/fix the issue because you might be touching down harder than expected.
Luckily pilots are trained to look at the green triangles (representing the Landing Gear Control & Interface Unit (LGCIU) status shown on the Wheel page)(bottom row images). If you have at least one green triangle on each gear you are good to go.