How to fix auth/invalid-phone-number in Firebase

E.164 format is: [+][country code][phone number with no spaces or dashes]

Examples of correct formats:
- United States: +1 650-555-3434 → +16505553434
- United Kingdom: +44 7444 555 666 → +447444555666
- Germany: +49 30 123456 → +4930123456

Remove all spaces, dashes, parentheses, and other formatting characters. Keep only the "+" prefix and digits.

Ensure you have the correct country code for the user's location. Country codes vary by nation:
- USA/Canada: +1
- UK: +44
- Germany: +49
- France: +33
- Australia: +61

Double-check the country code against the user's actual location. If unsure, ask the user to select their country in your app before submitting the phone number.

During development, Firebase allows you to register test phone numbers in the Firebase Console:

1. Open Firebase Console → Authentication → Sign-in method
2. Click on "Phone" provider
3. Expand "Phone numbers for testing"
4. Add a test phone number (e.g., +1 650-555-3434) with a test verification code (e.g., 123456)

When you use a registered test phone number, Firebase will not send an actual SMS. Instead, it will immediately verify with the code you specified.

Catch and handle the error properly to inform users:

JavaScript/Web:

try {
  await firebase.auth().signInWithPhoneNumber(
    "+1 650-555-3434",
    appVerifier
  );
} catch (error) {
  if (error.code === "auth/invalid-phone-number") {
    console.error("Invalid phone format. Use: +[country][number]");
  }
}

Flutter:

await FirebaseAuth.instance.verifyPhoneNumber(
  phoneNumber: "+1 650-555-3434",
  verificationFailed: (FirebaseAuthException e) {
    if (e.code == "invalid-phone-number") {
      print("Please enter a valid phone number with country code.");
    }
  },
);

React Native:

try {
  await auth().signInWithPhoneNumber("+1 650-555-3434");
} catch (error) {
  if (error.code === "auth/invalid-phone-number") {
    setError("Phone number format is invalid");
  }
}

Ensure the Phone authentication provider is enabled in your Firebase project:

1. Go to Firebase Console
2. Select your project
3. Navigate to Authentication → Sign-in method
4. Look for "Phone" in the list
5. If it's disabled (greyed out), click it and toggle "Enable"
6. Click Save

Without enabling the Phone provider, all phone authentication requests will fail.