Log into the device via terminal and type info to see the exact hardware revision. Step-by-Step Download Process
Choose between UniFi (WiFi/Switching), UISP (ISP/Wireless), or Protect (Cams). Download Firmware Ubiquiti
Ensure you aren't trying to flash "Global" firmware onto a "US" locked device (or vice versa), as some wireless frequencies are region-restricted. Conclusion Log into the device via terminal and type