Hi there! I understand you're having trouble saving a 720p video to your mobile device's gallery through the PixVerse app, and your device freezes when using the app. Let's work together to get this sorted out.

First, could you tell me a bit more? For example:
- Is your mobile device running Windows 10, or is this happening on a different device?
- Have you checked if PixVerse has permission to access your device’s storage?
- When exactly does the device freeze (e.g., when watching the ad, during download, or after)?
- Have you tried closing other apps to free up memory or restarting your device?

Meanwhile, let's try some initial steps that typically help with these issues:

1. Check App Permissions:
- Ensure PixVerse has permission to access your storage/gallery. You can usually find this in your device’s settings under Apps > PixVerse > Permissions.

2. Clear Cache and Data for PixVerse App:
- Sometimes cached data can cause freezing or download issues. Go to Settings > Apps > PixVerse, then clear the cache and, if possible, the data.

3. Close Background Apps:
- Closing other apps to free up memory might reduce freezing.

4. Refresh or Restart the App:
- Try closing the app completely and reopening it. Sometimes refreshing the page in the app fixes video download issues.

If these don't work, we can look into more advanced steps like checking the app’s version or reinstalling it. Also, if the ad isn’t triggering the video download, it could be related to account or server issues.

Let me know how these suggestions go or if you’ve already tried any of them! I’m here to help you every step of the way.