Hi there! I understand that you're experiencing an "invalid form submission" error when trying to sign in to the AMC app, while the website works fine for you. Let's work through this together.

Here are a few steps you can try to resolve the issue:

1. Clear the App Cache:
- Go to your device’s settings.
- Find the AMC Theatres app in the application section.
- Tap on it and look for an option to clear the cache. This can sometimes fix issues with the app.

2. Force Stop the App:
- In the same section of your device settings, you can force stop the app.
- Once it’s stopped, reopen the app and try to sign in again.

3. Uninstall and Reinstall the App:
- If the above steps don’t work, I recommend uninstalling the app completely.
- Restart your device.
- Then, go back to the app store and download the AMC Theatres app again.

4. Network Connection:
- Ensure you have a stable internet connection. Sometimes switching from Wi-Fi to mobile data (or vice versa) can help resolve connectivity issues.

5. Static IP Address:
- Some users have found it helpful to use a static IP address for their internet connection. You might want to try disabling Wi-Fi and using your mobile data to see if that makes a difference.

If these steps don't resolve the issue, it may be best to contact our support team directly for more assistance at [email protected].

Please let me know if any of these steps help or if you have any further questions!