Hi there! I understand you're having trouble completing trip planning on both the Amtrak app and website on your iPhone running iOS 15.8.4. Let's work together to get this sorted out.

To better assist you, could you please share a bit more detail about the issue? For example:
- Are you unable to enter trip details, or does the process freeze at a certain step?
- Is there an error message showing up?
- Does the payment or confirmation button fail to respond?
- Have you tried any steps already, like refreshing the app or restarting your device?

This info will help me tailor the fix for your specific situation. Meanwhile, here are some common steps that often resolve trip planning issues:

1. Update the Amtrak app: Make sure you have the latest version installed, as updates often fix bugs.
2. Clear app cache and restart app: On iPhone, you can close the Amtrak app completely by swiping it away and then reopen it.
3. Check internet connection: Trip planning requires a stable connection; try switching between Wi-Fi and cellular data.
4. Restart your iPhone: This can clear temporary glitches.
5. Try using Safari browser: Since your OS is iOS 15, use the latest version of Safari, and ensure JavaScript is enabled in settings. Sometimes desktop sites work better if you enable "Request Desktop Website" in Safari’s share menu.
6. Log out and back in: This refreshes your account session and may solve syncing issues.

If after trying these the problem persists, there could be a temporary server-side issue or a bug affecting both platforms. We can try further advanced troubleshooting then or you might want to contact Amtrak support directly for account-specific help.

Let me know what you’ve tried and the exact behavior you’re seeing, and we’ll keep going from there!