Hello! It sounds like you're having trouble logging into Jack's using Facebook. Let's work through this together.

To start, could you please let me know what error message you're seeing when you attempt to log in? Additionally, have you tried logging in with Facebook on other applications or websites, and did that work out for you? This will help us determine if it’s an issue related to Jack's or something more general with your Facebook account.

In the meantime, here are some steps you can try, which often help with login issues:

1. Clear Browser Cache and Cookies: On your WebKit browser, go to settings and find the option to clear cache and cookies. This will remove any potentially corrupted files that may be causing the issue.

2. Reboot Your Device: After clearing the cache, restart your Android device. Sometimes a simple reboot can resolve login issues.

3. Check Facebook's Status: Sometimes, Facebook may have outages or issues. You can check their status on Downdetector to see if there are widespread problems.

4. Update the App: Make sure that you’re using the latest version of the Jack's app. You can check on the Google Play Store to see if there are any updates available.

Please give these a try and let me know if the issue persists or if you discover any error messages. I’m here to help!