Hi there! I understand you're having trouble logging into your Letsfit app because it's saying your email is not registered, and when you try to register, it doesn't allow you either. Let's work through this together.

First, can you confirm a couple of things for me?
- Have you used this email with the Letsfit app before, or is this the first time trying to register?
- Have you tried using the "Forgot Password" option with your email to see if it recognizes it for password reset?
- Also, do you currently have the latest version of the Letsfit app installed on your iPhone running iOS 18.7?

Once I have these details, I can guide you step-by-step to resolve this. Meanwhile, here are some quick initial steps to try:

1. Check if your email is correctly typed when logging in or registering—sometimes a small typo can cause this issue.

2. Use the "Forgot Password" feature on the login screen:
- Open the Letsfit app.
- Tap "Forgot Password" and enter your email.
- See if you receive a reset email. If you do, follow the instructions to reset your password and login.

3. Try uninstalling and reinstalling the Letsfit app to clear any cached data that might be causing the problem:
- On your iPhone, tap and hold the Letsfit app icon.
- Tap "Remove App" > "Delete App."
- Go to the App Store and reinstall the Letsfit app.
- Try logging in again.

4. Check your device's time settings, sometimes incorrect time format can cause login issues:
- Go to Settings > General > Date & Time.
- Make sure "Set Automatically" is ON.
- Try switching between 12-hour and 24-hour formats if possible, then try logging in again.

If after these steps you still get the "email not registered" error, it's possible there might be an issue with your account in our system or a server-side glitch.

If so, please let me know, and I can help you escalate this further or guide you on contacting Letsfit support directly for account verification.

How does that sound? Let me know what you’ve tried and how I can assist next!