Google map api shows request in console but gives me 400 for bad key

Trying to load photorealistic tiles but google map api but get below error. Console shows requests as all failed. Am i missing anything, sticking to CesiumJS: Photorealistic 3D Tiles from Google Maps Platform – Cesium. Key is fine for JavaScript api

“code”: 400,
“message”: “API key not valid. Please pass a valid API key.”,