Hi there! I see you're having trouble logging in to the Tandem app on your iPhone. To help you better, could you tell me a bit more about what happens when you try to log in? For example, do you get an error message, does the app just reload, or is the login button unresponsive?

While I wait for those details, here are some initial straightforward steps we can try:

1. Check your login method and email – Sometimes login issues happen if the app is expecting a different login method (email/password, social login) or if there is a typo in your email address.

2. Restart the app – Swipe up from the bottom (or double-click home button if available) and close the Tandem app completely, then reopen it.

3. Verify internet connection – Make sure your iPhone has a stable internet connection via Wi-Fi or cellular data.

4. Update the app – Check the App Store for any pending Tandem app updates and install them to ensure compatibility with iOS 18.5.

5. Reinstall the app – If the above don't help, delete the Tandem app and reinstall it from the App Store. This often resolves issues caused by corrupted cache or outdated files.

Please try these and let me know what you see or if you get any specific error messages. That will help me guide you through more detailed troubleshooting if needed!

Are you able to provide me with what you see on screen when you try to log in?