Hi there! Thanks for reaching out. I understand you just installed and registered the Whering app on your iPhone running iOS 18.3, but when you try to open it, you only see a black screen. Let's get this sorted for you.

To start, could you let me know if this black screen appears immediately after launching the app, or does some loading indicator show up first? Also, have you tried closing the app completely and reopening it? Knowing what steps you've tried will help me guide you better.

Meanwhile, here are some useful troubleshooting steps for your iPhone:

1. Force Close and Reopen the App:
- Swipe up from the bottom (or double-click the Home button) to open the app switcher.
- Swipe up on the Whering app to close it completely.
- Reopen the app and see if the screen loads.

2. Check for App Updates:
- Open App Store, tap your profile icon at the top right.
- Scroll to see if Whering has an update. If yes, update it.

3. Restart Your iPhone:
- Press and hold the side button and either volume button until the slider appears.
- Slide to power off, wait 30 seconds, then power it back on.

4. Reinstall the App:
- Press and hold the Whering app icon, tap 'Delete App'.
- Reinstall from the App Store, then log in again.

5. Check App Permissions:
- Go to Settings > Whering.
- Ensure necessary permissions like Storage, Camera, or Network are enabled.

If these don't help, it could be a compatibility or account-related issue. I'll be happy to dig deeper with you or escalate this if needed.

Could you please try these and let me know? Also, if the problem happens after a certain action or screen, that info will help me.