Troubleshooting Firebase Cloud Messaging Connectivity Issues in iOS

This guide outlines common steps to troubleshoot Firebase Cloud Messaging (FCM) connectivity issues in iOS apps specifically when encountering issues receiving push notifications on cellular data. Even if the FCM diagnostic reports a 'connected' status, there might be underlying network or configuration problems preventing notification delivery.

**Understanding the Problem:**

You've successfully received FCM push notifications over Wi-Fi but encounter issues when switching to cellular data. The diagnostic log indicates a 'connected' status, suggesting that the connection itself isn't the primary obstacle.

**Possible Causes:**

* **App Permissions:** Ensure your app has necessary permissions to receive notifications in the background even when using cellular data. Navigate to
* **Settings > Notifications >[Your App Name]**
* Verify 'Allow Notifications' is ON.
* Confirm 'Notification Center' and 'Lock Screen' are enabled.
* **Background App Refresh:** While not directly related to FCM, Background App Refresh can sometimes interfere with push notifications.
* Go to **Settings > General > Background App Refresh**
* Ensure your app's Background App Refresh is enabled.

* **Cellular Data Not Allowed:** Check your device's cellular data settings to ensure that cellular data is allowed for your app.
* Go to **Settings > Cellular**
* Swipe to confirm your app is allowed to use cellular data.

* **Firewall Restrictions:** If you're using a firewall or VPN, it might be blocking FCM connections. Review your firewall settings and ensure ports needed for FCM communication are open. Consult your firewall provider's documentation for specific port numbers.

* **APN Settings:** Incorrect or outdated Access Point Name (APN) settings can impact cellular data connectivity. Ensure your device's APN is properly configured for your carrier.

**Troubleshooting Steps:**

1. **Restart your device:** Often, a simple restart can resolve temporary glitches.
2. **Check internet connectivity:** Ensure you have a stable cellular data connection.
3. **Check app notifications:** Verify that your app's notification settings are properly configured.
4. **Verify device orientation:** Some devices have issues receiving notifications if they are in a specific orientation.
5. **Update your app:** Make sure you're using the latest version of your app, which may contain bug fixes.
6. **Clean build:** Try deleting the app from your device and reinstalling it with a fresh build.
7. **Check FCM logs:** Analyze the FCM logs for any errors or warnings that might provide insights into the issue.
8. **Test on different devices:** If possible, test the app on different devices with varying network configurations.

**Seeking Further Assistance:**
If you've exhausted these troubleshooting steps and are still facing issues, consider reaching out to the Firebase support team for more specialized assistance.

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