Hi there! Congratulations on your new BLACKPINK LIGHT STICK v2! I see you're updating the firmware, but it’s stopped at 8.5%. Let's work together to get it sorted out.

First, to help me guide you better:
- Are you updating via the official app or another method?
- Is your phone's Bluetooth connection stable and permissions for the app properly set?
- Have you tried restarting both your phone and the light stick since starting the update?

Meanwhile, here is a reliable step-by-step to try:
1. Remove the batteries from the light stick, wait about 10 seconds, then reinsert them. This reset sometimes clears the stalled update.
2. Make sure the batteries are fresh; weak batteries may cause update failures.
3. Restart your phone to refresh the Bluetooth connection.
4. Open the BLACKPINK app and try to re-initiate the firmware update.
5. Keep your phone close to the light stick during the update to maintain a stable connection.

If the update still stalls at 8.5%, it could be useful to uninstall and reinstall the BLACKPINK app to clear any app cache issues.

If after these steps the issue persists, we might need to look into any possible interference or deeper troubleshooting steps.

Let me know how these go or if you need help with any of the steps!