To resolve the issue of not being able to load watch faces on your Apple Watch Series 8 and receiving the "not available" message, follow these steps:

1. Restart Your Apple Watch: A simple restart can often resolve many software issues. Hold down the side button and the Digital Crown until the Apple logo appears.

2. Check Your Connection: Ensure that your Apple Watch is connected to your iPhone. On your iPhone, go to the Bluetooth settings and confirm that your Apple Watch is listed and is connected.

3. Update Your Software: Ensure both your iPhone and Apple Watch are running the latest software. On your iPhone, go to Settings > General > Software Update and check for any available updates. For your Apple Watch, open the Watch app, go to General > Software Update.

4. Limit Shared Photos: If you have photo-sharing enabled with your watch, consider limiting the number of photos. Some users found that reducing the number of shared photos to 25 solved similar problems. Disable photo sharing in the Watch app on your iPhone at My Watch > Photos and check if this resolves the issue - learn more.

5. Close and Reopen the Watch App: Exit the Watch app on your iPhone, then reopen it. This can help refresh any settings and sync the watch faces properly - learn more.

6. Resync Your Watch: Go to the Watch app on your iPhone, tap on My Watch, and scroll down to the bottom. Find "Unpair Apple Watch" and tap it. After unpairing, reconnect your watch following the on-screen prompts. This can reset any connectivity issues - learn more.

7. Clearing Complications and Faces: If specific complications are problematic, remove them and try re-adding them after the faces load. This might help in restoring the functionality.

8. Check for Restrictions: Make sure that there are no parental controls or restrictions set that may limit the functionalities on your watch.

If these steps do not work, there may be a deeper software issue, and reaching out to Apple Support for further assistance would be advisable.