Please make sure your Airport Extreme is not set to bridge mode as DNS changes will not work. Instead set DNS on your main router or remove bridge mode.
- Open Airport Utility found in Applications > Utilities
- Select the Airport Extreme from the menu and click edit
- Select the Internet Tab
- In DNS servers input 184.108.40.206 and 220.127.116.11
- Click update and wait for the Airport Extreme to restart
- Restart the devices connected to the Airport Extreme that you want to use with our DNS
First step of troubleshooting should always be to restart device(s) and router. Then check your setup status in your SmartDNS dashboard.