How to Fix Firebase Phone Verification

In this tutorial, you'll learn about How to Fix Firebase Phone Verification. We cover key concepts, practical examples, and best practices.

Firebase phone authentication fails — the SMS code is not delivered, reCAPTCHA does not load, or verification returns "invalid-verification-code."

The Wrong Way

// Requesting SMS on every click without debouncing
firebase.auth().signInWithPhoneNumber(phone, recaptchaVerifier);

Multiple requests in quick succession trigger Firebase's rate limiting, blocking SMS delivery for hours.

The Right Way

Step 1: Set up reCAPTCHA correctly

// Initialize reCAPTCHA once on page load:
const recaptchaVerifier = new firebase.auth.RecaptchaVerifier(
  'recaptcha-container', // div ID
  {
    size: 'normal', // 'invisible' for no interaction
    callback: () => {
      // reCAPTCHA solved
    }
  }
);

// Render the reCAPTCHA:
recaptchaVerifier.render().then(widgetId => {
  window.recaptchaWidgetId = widgetId;
});

Step 2: Request SMS with proper debouncing

let lastRequestTime = 0;

async function requestPhoneVerification(phoneNumber) {
  // Prevent rapid re-requests (30 second cooldown)
  const now = Date.now();
  if (now - lastRequestTime < 30000) {
    alert('Please wait 30 seconds before requesting a new code');
    return;
  }
  lastRequestTime = now;

  try {
    const confirmationResult = await firebase.auth()
      .signInWithPhoneNumber(phoneNumber, recaptchaVerifier);
    window.confirmationResult = confirmationResult;
    alert('SMS sent!');
  } catch (error) {
    console.error('SMS request failed:', error);
  }
}

Step 3: Handle SMS code confirmation

async function confirmCode(code) {
  try {
    const result = await window.confirmationResult.confirm(code);
    console.log('Phone verified, user:', result.user.uid);
  } catch (error) {
    if (error.code === 'auth/invalid-verification-code') {
      alert('Incorrect code. Please try again.');
    }
  }
}

Step 4: Use invisible reCAPTCHA for better UX

const recaptchaVerifier = new firebase.auth.RecaptchaVerifier(
  'phone-sign-in-button', // button ID
  {
    size: 'invisible',
    callback: () => {
      // Auto-proceed when reCAPTCHA passes
      requestPhoneVerification(phoneNumber);
    }
  }
);

Phone verification working — SMS received in under 10 seconds, code confirmed, user authenticated.

Prevention

• Always test phone auth in a Firebase project with a real phone number (test numbers may be blocked).
• Add a "Resend code after 30s" button following your cooldown logic.
• The phone verification pattern is built into Doda Browser's account recovery — SMS-based 2FA with rate limiting to prevent abuse.

Common Mistakes with auth phone verification

1. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors
2. Non-exhaustive pattern matches that compile with warnings then crash at runtime
3. Misunderstanding that String is [Char] with poor performance for large text operations

These mistakes appear frequently in real-world FIREBASE code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

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