Hi! I see you're having trouble downloading the Planet Fitness app on your iPhone. Let's get this sorted out together. Could you tell me a bit more about what happens when you try to download the app? For example, do you see an error message, does it get stuck, or does nothing happen at all?

Meanwhile, I'll guide you through some common fixes for app download issues on iOS 15.8.4:

1. Check Your Internet Connection:
Ensure you have a stable Wi-Fi or cellular data connection. Sometimes weak or intermittent internet can cause downloads to fail.

2. Restart Your iPhone:
Press and hold the power button and slide to power off, then turn it back on. This can clear temporary glitches.

3. Check Available Storage:
Go to Settings > General > iPhone Storage to ensure you have enough free space for the app.

4. Sign Out and Back In to the App Store:
- Go to Settings > App Store
- Tap your Apple ID and choose Sign Out
- Then sign back in and try downloading again.

5. Update iOS if Possible:
Though you're on iOS 15.8.4, you might want to check if any minor updates are pending under Settings > General > Software Update. Sometimes updating helps fix app compatibility.

6. Try Downloading the App Directly from the App Store Link:
Use this direct link to the Planet Fitness app on the App Store: Planet Fitness on the App Store

If you get any error messages during these steps, please share them with me, so I can help troubleshoot further.

Are you alright going through these steps? Or have you tried some already? Let me know!