Why isn't Firebase sending an OTP email for authentication in my Expo React Native app?

Below is an explanation of the problem and how to fix it.

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What’s Happening

You’re using the password reset API (sendPasswordResetEmail and confirmPasswordReset) to send an OTP code for sign‑in. In Firebase Auth, the password reset flow is meant for setting a new password (via a link emailed to the user) rather than authenticating a user via an OTP.

Firebase provides other email flows such as email link authentication (magic links). With email link auth, a link is sent to the user’s email. When the user clicks the link (or uses it in your app), Firebase identifies and authenticates the user.

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How to Fix It

If you want to allow users to sign in via email without a password (magic link), you can use the email link sign‑in method rather than the password reset flow. Here’s how you can do it:

1. Send the email sign‑in link
   Use the sendSignInLinkToEmail method (or the equivalent from the Firebase SDK you use) to send an action link to the user’s email. You must include the appropriate action code settings such as the URL to which the link should redirect.

2. Handle the sign‑in link in your app
   When the user clicks the link, the app should detect that the link is a sign‑in link (using isSignInWithEmailLink) and then finish the sign‑in process by calling signInWithEmailLink.

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Example Code

Below is an example of how you might implement email link sign‑in in an Expo React Native app using the modular Firebase SDK. (Make sure you have set up your dynamic links and action code settings properly in your Firebase Console.)

JAVASCRIPTCopied
import React, { useEffect, useState } from "react";
import { TextInput, TouchableOpacity, Text, View, Alert } from "react-native";
import { getAuth, isSignInWithEmailLink, sendSignInLinkToEmail, signInWithEmailLink } from "firebase/auth";
import { firebaseApp } from "../../firebaseConfig"; // Your initialized firebase instance

const auth = getAuth(firebaseApp);

const EmailLinkSignIn = () => {
  const [email, setEmail] = useState("");
  const [linkSent, setLinkSent] = useState(false);

  // Action code settings: make sure your "url" is whitelisted in the Firebase Console
  const actionCodeSettings = {
    // URL you want to redirect back to after sign in is completed.
    url: "https://your-app-page.com/finishSignIn",
    // This must be true.
    handleCodeInApp: true,
    // For mobile apps, you can provide additional information if needed.
    // iOS: { bundleId: "com.example.ios" },
    // android: { packageName: "com.example.android", installApp: true, minimumVersion: "12" },
  };

  // Send the email link
  const sendLink = async () => {
    try {
      await sendSignInLinkToEmail(auth, email, actionCodeSettings);
      // Save the email locally so that you have it later to complete sign in
      // This is important if the user opens the link on the same device.
      window.localStorage.setItem('emailForSignIn', email);
      setLinkSent(true);
      Alert.alert("Success", "The sign-in email has been sent.");
    } catch (error) {
      Alert.alert("Error", error.message);
    }
  };

  // Handle the incoming email link after user clicks it
  const completeSignIn = async (incomingLink) => {
    if (isSignInWithEmailLink(auth, incomingLink)) {
      let storedEmail = window.localStorage.getItem('emailForSignIn');
      if (!storedEmail) {
        // If email is not available (user opened on a different device), ask for it:
        storedEmail = prompt("Please provide your email for confirmation");
      }
      try {
        const result = await signInWithEmailLink(auth, storedEmail, incomingLink);
        window.localStorage.removeItem('emailForSignIn');
        Alert.alert("Success", "Signed in successfully.");
        // You can access result.user and result.additionalUserInfo here.
      } catch (error) {
        Alert.alert("Error", error.message);
      }
    }
  };

  useEffect(() => {
    // Assume incomingLink is obtained via deep linking or similar mechanism.
    // For example, you might get it from: 
    // Linking.getInitialURL().then(url => { if (url) completeSignIn(url); })
    // The implementation depends on your deep linking setup.
  }, []);

  return (
    <View style={{ padding: 20 }}>
      {!linkSent ? (
        <>
          <Text>Enter your email to receive a sign-in link:</Text>
          <TextInput
            placeholder="Email"
            value={email}
            onChangeText={setEmail}
            style={{ borderWidth: 1, marginVertical: 10, padding: 8 }}
          />
          <TouchableOpacity onPress={sendLink} style={{ backgroundColor: "#2196F3", padding: 10 }}>
            <Text style={{ color: "#fff" }}>Send Sign-In Link</Text>
          </TouchableOpacity>
        </>
      ) : (
        <Text>Please check your email for the sign-in link.</Text>
      )}
    </View>
  );
};

export default EmailLinkSignIn;

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Key Points

• Password Reset vs. Email Link Sign-In:
  The password reset flow is intended for resetting user passwords via a link. It is not designed for OTP-based sign-in.

• OTP via Email:
  Firebase does not provide an out‑of‑the‑box OTP (numeric code) sent via email for authentication. For email sign‑in, use email link authentication. If you require a numeric OTP, you would need to develop a custom solution using a third‑party email service.

• Deep Linking:
  For email link authentication to work in a mobile app, ensure your app is properly set up for deep linking. This allows the app to handle the incoming email action link.

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By switching to email link authentication and ensuring you have the necessary deep linking and action code settings in place, you should be able to successfully send a sign‑in link to your users’ email addresses.