How to fix PERMISSION_DENIED: Missing or insufficient permissions. in Firebase

import { getAuth } from "firebase/auth";

const auth = getAuth();
if (auth.currentUser) {
  console.log("User is logged in:", auth.currentUser.email);
} else {
  console.log("User is not authenticated");
  // Call sign in function before accessing Firestore
}

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write: if request.auth != null;
    }
  }
}

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    // Allow users to read/write their own user document
    match /users/{userId} {
      allow read, write: if request.auth.uid == userId;
    }
    
    // Allow anyone authenticated to read posts
    match /posts/{postId} {
      allow read: if request.auth != null;
      allow create: if request.auth != null;
      allow update, delete: if request.auth.uid == resource.data.authorId;
    }
  }
}

// Client-side (subject to security rules)
import { getFirestore, collection, query, where, getDocs } from "firebase/firestore";
const db = getFirestore();
const q = query(collection(db, "users"), where("active", "==", true));
const snapshot = await getDocs(q);

// Server-side (bypasses security rules)
import admin from "firebase-admin";
const db = admin.firestore();
const snapshot = await db.collection("users").where("active", "==", true).get();

import { getFirestore, collection, addDoc, getDoc, doc } from "firebase/firestore";
const db = getFirestore();

try {
  // Write document
  const docRef = await addDoc(collection(db, "users"), { name: "John" });
  
  // Wait for write to complete, then read
  const docSnap = await getDoc(doc(db, "users", docRef.id));
  if (docSnap.exists()) {
    console.log("Document:", docSnap.data());
  }
} catch (error) {
  console.error("Error:", error.message);
}