Hello! I understand that the sound stopped working on your Breathing Plan in the Oxygen Advantage app on your iPhone. Let's try to get that fixed for you.

First, just to clarify a couple of things before we dive in:
- Is the sound not playing only in the Breathing Plan section, or do you experience sound issues elsewhere in the app or on your device?
- Have you already tried any fixes like restarting the app or your phone?

Once I have a bit more info, we can go step-by-step. Meanwhile, here’s a basic troubleshooting approach that often helps:

1. Check the iPhone Volume and Mute Switch:
Make sure your device volume is up and the mute switch (the physical switch on the side) isn’t enabled.

2. App Sound Settings:
Sometimes app-specific sound settings can be toggled off. Open the Oxygen Advantage app, and check if there is an in-app sound or audio setting that may have been muted.

3. Restart the App:
Fully close the Oxygen Advantage app by swiping it away from the app switcher, then reopen it and test the Breathing Plan sound again.

4. Restart Your iPhone:
A simple restart can often resolve temporary glitches affecting audio playback.

5. Check iOS Permissions:
Go to your iPhone’s Settings > Oxygen Advantage and ensure “Microphone” and any relevant permissions related to sound or notifications are enabled.

6. Check Media & Notifications Volume:
Sometimes media volume is separate from ringer volume, so try adjusting media volume while playing the breathing plan.

If you try these and the sound still doesn’t work only in the Breathing Plan, it might be a specific app glitch or a problem with the particular breathing plan file.

Let me know how these steps go or if anything here feels unfamiliar, and I can guide you further!