To resolve the issue of not being able to check in on MyFrontier and receiving an error code, follow these steps:

1. Identify the Error Code: Start by noting the specific error code displayed. This can help in understanding the exact issue you are encountering.

2. Check Internet Connection: Ensure that your device is connected to the internet. A poor or unstable connection can lead to issues while trying to check in.

3. Restart the App: Close the MyFrontier app completely and then restart it. This can resolve any temporary glitches that may be causing the error.

4. Update the App: Make sure you have the latest version of the MyFrontier app installed. Go to the App Store on your iPhone, search for "MyFrontier," and check for any available updates.

5. Clear App Cache: If the problem persists, try clearing the app's cache. You can do this by uninstalling the app and then reinstalling it.

6. Check Service Status: Visit the Frontier service status page or check their social media channels for any announcements related to service outages or maintenance that might affect your ability to check in.

7. Contact Customer Support: If none of the above steps work, reach out to MyFrontier customer support. Provide them with the error code you received, as well as the steps you have already taken. This will help them assist you more efficiently.

By following these steps, you should be able to resolve the issue with checking in on MyFrontier.