Official downloads for version 5.5.6 have been largely replaced by newer versions like v6.3.24 on the Ubiquiti Downloads page
While newer versions like airOS 6 and airOS 8 exist, some users retain v5.5.6 for specific stability requirements or to maintain compatibility with older network segments. Supported Devices Ubnt Firmware Xw.v5.5.6 Download
Do NOT turn off the device during the flashing process. The radio will restart automatically. Important Considerations & Safety Official downloads for version 5