Hello @Palani, In the Firebase, there are two types of storage,
- Cloud Firestore (Very recent one & NoSQL database)
- Realtime Database (To which we upload the data using NodeMCU)
In the Arduino Code, you can see that there is a variable named FIREBASE_AUTH.
This variable should be assigned to the Database secret. This you can find in Project Settings -> Service accounts -> Database Secrets.
My mistake is, i have mistakenly assigned thay to Web API key. This is found at Project Settings -> General.
The error can also occur when u don't initialise a proper realtime database in Firebase. (This is not my case).