Hi there! I understand you're having trouble opening the Visible app on your iPhone while trying to add cellular service to your Apple Watch Ultra. Let's get that sorted out together.

First, can you let me know if the Visible app was working fine before this, or is it not opening at all ever since you started the setup? Also, what iPhone model and iOS version are you using? This will help me guide you precisely.

Meanwhile, here are some general steps we can try to get the Visible app up and running on your iPhone:

1. Close and Reopen the App
- Double-click the Home button or swipe up from the bottom (depending on your model) to see recent apps.
- Swipe the Visible app off the screen to close it completely.
- Then tap the app icon again to open it.

2. Restart Your iPhone
Sometimes a simple restart clears up minor glitches. Press and hold the power button, slide to power off, wait 30 seconds, then turn it back on.

3. Update the App and iOS
Make sure your Visible app is updated to the latest version via the App Store. Also, check if your iPhone’s iOS is up to date (Settings > General > Software Update).

4. Reinstall the Visible App
If it still won't open, uninstall the app: press and hold the app icon until it wiggles, tap the "X" or Remove App, then reinstall it from the App Store.

Once the app opens successfully, you can proceed with the Apple Watch cellular setup:

- Open the Watch app on your iPhone.
- Tap the “Cellular” tab and select “Set up Cellular.” This action should open the Visible app.
- Follow the prompts to add your Apple Watch Ultra to the cellular plan.

If after trying these the Visible app still won’t open, or if the setup process fails, a useful tip is to unpair your Apple Watch from your iPhone and then restart both devices before trying again. Unpairing resets some settings that might be blocking the connection1 2.

Could you please try the above and let me know what happens? If there’s any error message or behavior you see, sharing that would help me pinpoint the issue better.