Hi! I see you're running into an issue where your check-in process with Frontier Airlines is stuck at 99% and then locks up. I'd love to help you get this sorted out.

To start, can you tell me if you’re using the Frontier app or the website on your iPhone? Also, are you connected through Wi-Fi or cellular data? Sometimes connection interruptions can cause the process to hang.

In the meantime, here are some initial steps we can try to resolve the issue:

1. Force quit the app or browser you are using for check-in and then reopen it. On iOS 18.4.1, you can swipe up from the bottom of the screen and pause, then swipe the app off the screen to close it.

2. Clear cache or try a different browser if you’re using Safari or Chrome. Safari’s cache can be cleared by going to Settings > Safari > Clear History and Website Data.

3. Restart your iPhone. Sometimes a simple restart helps reset any minor glitches.

4. Ensure your app or browser is updated to the latest version.

5. Try checking in with a fresh session: Open a private/incognito browsing window or reinstall and open the Frontier app again, then attempt check-in.

If the issue persists, it could be related to the seat assignment system. Frontier sometimes assigns “Zone 99” or Seat 0 during check-in when automatic seat selection hangs or processes incompletely, which may cause a lockup at 99% completion1.

To avoid this, if you haven't already, try manually selecting your seat during check-in if the option is available, or wait a bit and try checking in again closer to the 24-hour window before your flight.

Could you also confirm if you have a seat assigned already, or if you’re waiting on seat selection during check-in? That will help me provide more tailored advice.

Let me know what you find and we can go from there!

My seat is already assigned

Thanks for letting me know your seat is already assigned. That’s helpful information!

Since your check-in is locking up at 99% even though you already have an assigned seat, here are some next steps tailored to this:

1. Double-Check Your Seat Assignment: Sometimes the system may have a glitch recognizing seat assignments. You can verify your seat by logging into your booking on the Frontier app or website and reviewing your itinerary or seat map.

2. Try Another Network Connection: If you are on Wi-Fi, try switching to cellular data or vice versa. Sometimes network issues can cause the final check-in step to stall.

3. Update or Reinstall the App: Since you’re on iOS 18.4.1, make sure your Frontier app is updated to the latest version from the App Store. If it is, try uninstalling and reinstalling it fresh.

4. Use a Different Device or Browser: If possible, try completing check-in from a different device (like a computer) or a different browser on your iPhone, such as switching from Safari to Chrome, to see if it gets past 99%.

5. Clear App Cache or Browser Cookies: For Safari, go to Settings > Safari > Clear History and Website Data. This can resolve data conflicts causing the hang.

6. Attempt Early or Slightly Delayed Check-in: Frontier’s system sometimes has delays or hiccups exactly at the 24-hour check-in opening or peak periods. You might try logging in a bit earlier or a bit later than the usual 24 hours before your flight.

If none of these suggestions resolve the issue, there may be a backend issue with your booking or account that requires intervention. In that case, I’d recommend contacting Frontier’s support directly at [email protected] with your booking reference and a brief description of the problem.

Feel free to try these and let me know how it goes! Are you comfortable with any of these steps, or do you want me to guide you through one of them in detail?