We upgraded our system last week to v15.5 and now our Polycom phones will not provision or register after manual phone configuration. The following steps have been followed: Download latest Polycom files Verify DHCP Option 66 configured for http://***.***.***.***:5000/provisioning/*********** Factory Reset Phone Update the Firmware to 4.0.10.0689 Boot Block 3.0.2.0024 Updater 5.0.10.0028 Configure Phone in 3CX Reboot phone Phone loads to the default factory screen (SoundPointIP). It has the correct Boot server url. Important to note that the phones are connecting over a VPN to the phone system. The network configuration worked perfectly on v14.x for approximately 150 phones which all connect over VPN tunnels. Furthermore, most phones are working fine however if they need to update their configuration for some reason they will not configure.