How to fix auth/invalid-dynamic-link-domain: Dynamic link domain not configured in Firebase

First, verify that Dynamic Links is enabled for your Firebase project:

1. Go to the [Firebase Console](https://console.firebase.google.com/)
2. Select your project
3. In the left sidebar, click on "Dynamic Links"
4. If you see a "Get Started" button, click it to enable Dynamic Links
5. If it's already enabled, you'll see your existing dynamic links

If Dynamic Links isn't enabled, you need to enable it before proceeding.

Configure your dynamic link domain:

Option A: Use a free page.link subdomain (recommended for testing):

1. In Firebase Console > Dynamic Links
2. Click "Get Started" or "New Dynamic Link"
3. Firebase will automatically assign you a free subdomain like yourproject.page.link
4. Note this domain for use in your app

Option B: Use a custom domain:

1. In Firebase Console > Dynamic Links
2. Click "Add URL prefix"
3. Enter your custom domain (e.g., links.example.com)
4. Follow the DNS verification steps:
- Add the provided TXT record to your domain's DNS
- Wait for DNS propagation (can take up to 48 hours)
- Click "Verify" in Firebase Console

Important: The domain must use HTTPS and have a valid SSL certificate.

Update your Firebase Authentication code to use the correct domain:

For web apps (JavaScript/TypeScript):

import { getAuth, sendPasswordResetEmail } from "firebase/auth";

const auth = getAuth();
const actionCodeSettings = {
  // Use 'linkDomain' instead of deprecated 'dynamicLinkDomain'
  linkDomain: "yourproject.page.link", // Your configured domain
  // OR for custom domains:
  // linkDomain: "links.example.com",

  // Other required settings:
  url: "https://yourapp.com/reset-password", // Your app's reset page
  handleCodeInApp: true, // Set to true for mobile apps
};

// Example: Send password reset email
sendPasswordResetEmail(auth, "[email protected]", actionCodeSettings)
  .then(() => {
    console.log("Password reset email sent!");
  })
  .catch((error) => {
    console.error("Error:", error.code, error.message);
  });

For mobile apps (React Native/Flutter):
Configure your deep linking according to Firebase documentation.

Test your dynamic link configuration:

1. Send a test email:

// Send a password reset email to yourself
   sendPasswordResetEmail(auth, "[email protected]", actionCodeSettings);

2. Check the email:
- Open the password reset email
- Click the link
- Verify it redirects to your app correctly

3. Test on different platforms:
- Test on web browser
- Test on iOS device
- Test on Android device

4. Check Firebase Console logs:
- Go to Firebase Console > Authentication > Events
- Look for any errors related to dynamic links

If you're using the deprecated dynamicLinkDomain parameter, update your code:

Before (deprecated):

const actionCodeSettings = {
  dynamicLinkDomain: "yourproject.page.link", // DEPRECATED
  url: "https://yourapp.com/reset-password",
  handleCodeInApp: true,
};

After (correct):

const actionCodeSettings = {
  linkDomain: "yourproject.page.link", // CORRECT
  url: "https://yourapp.com/reset-password",
  handleCodeInApp: true,
};

Note: The dynamicLinkDomain parameter was deprecated because Firebase now supports custom Hosting link domains through the linkDomain parameter.

For mobile apps, ensure proper configuration:

iOS (Xcode project):
1. Open your Xcode project
2. Go to Target > Info > URL Types
3. Add a URL Scheme matching your bundle ID
4. Configure Associated Domains in Capabilities:
- Add: applinks:yourproject.page.link
- Or for custom domains: applinks:links.example.com

Android (AndroidManifest.xml):

<intent-filter>
  <action android:name="android.intent.action.VIEW" />
  <category android:name="android.intent.category.DEFAULT" />
  <category android:name="android.intent.category.BROWSABLE" />
  <data
    android:host="yourproject.page.link"
    android:scheme="https" />
</intent-filter>

Firebase Console configuration:
1. Go to Firebase Console > Project Settings
2. Add your iOS bundle ID and Android package name
3. Download updated config files for each platform