Hi! I understand your PiggyVest app on your iPhone running iOS 15.1 is not opening and crashes immediately when you tap on it. Let's work together to get this sorted out.

To start with, here are some steps tailored for your iPhone:

1. Force close the app and reopen
- Double tap your Home button or swipe up from the bottom and pause to see running apps.
- Find PiggyVest and swipe it up to close completely.
- Then tap the app icon to open it again.

2. Restart your iPhone
- Press and hold the side button and either volume button until you see the slider.
- Slide to power off your device.
- After it’s off, press and hold the side button to turn it back on, then try the app again.

3. Update the app
- Open the App Store, tap your profile picture, and scroll to see if PiggyVest has an update available.
- Installing the latest version can fix compatibility and bug issues.

4. Reinstall the app
- Press and hold the PiggyVest icon, tap “Remove App” > “Delete App” to uninstall.
- Then go back to App Store and download it again fresh.

5. Check available iOS Space and Software Updates
- Go to Settings > General > iPhone Storage to make sure you have enough space for the app to run smoothly.
- Also check Settings > General > Software Update to see if you should update your iOS version, as newer versions can improve app stability.

If after these steps the app still closes immediately, it may be due to a deeper compatibility or account issue. In that case, I can help you escalate or check if there's a known service issue for your region.

Could you please let me know if you have tried any of these already, or if anything changes after trying them? That way I can guide you further!