How to fix auth/invalid-argument: Invalid parameter passed to method in Firebase

import { getAuth, signInWithEmailAndPassword } from 'firebase/auth';

const auth = getAuth();
const email = userInput.email?.trim();
const password = userInput.password?.trim();

// WRONG: May have empty strings
// signInWithEmailAndPassword(auth, email, password);

// RIGHT: Validate first
if (!email || !password) {
  console.error("Email and password are required");
  return;
}

signInWithEmailAndPassword(auth, email, password)
  .catch((error) => console.error(error.message));

import { getAuth, signInWithEmailAndPassword } from 'firebase/auth';

const auth = getAuth();
signInWithEmailAndPassword(auth, email, password)
  .then((userCredential) => console.log(userCredential.user))
  .catch((error) => console.error(error.code, error.message));

import firebase from 'firebase/app';
import 'firebase/auth';

firebase.auth().signInWithEmailAndPassword(email, password)
  .then((userCredential) => console.log(userCredential.user))
  .catch((error) => console.error(error.code, error.message));

// WRONG: Parameter order incorrect
signInWithEmailAndPassword(password, auth, email);

// WRONG: Missing auth parameter (v9+)
signInWithEmailAndPassword(email, password);

// WRONG: Passing object instead of auth instance
signInWithEmailAndPassword({auth}, email, password);

// CORRECT: auth instance first, then email, then password
signInWithEmailAndPassword(auth, email, password);

import { initializeApp } from 'firebase/app';
import { getAuth } from 'firebase/auth';

// Initialize Firebase first
const app = initializeApp({
  apiKey: "YOUR_API_KEY",
  projectId: "YOUR_PROJECT_ID",
  // ... other config
});

// Get auth instance AFTER initializing app
const auth = getAuth(app);

// NOW you can use auth methods
import { signInWithEmailAndPassword } from 'firebase/auth';
signInWithEmailAndPassword(auth, email, password);

// WRONG: Not a real Firebase method
signInWithPhone(auth, number); // Should be signInWithPhoneNumber
auth.loginWithEmail(email, pwd); // Should be signInWithEmailAndPassword

// WRONG: Missing required parameters
createUserWithEmailAndPassword(auth); // Missing email and password

// CORRECT
signInWithPhoneNumber(phoneNumber, appVerifier);
signInWithEmailAndPassword(auth, email, password);
createUserWithEmailAndPassword(auth, email, password);