Yealink has shut down an old RPS service that was exclusively supporting EOL (end of life) devices. In addition most devices now have a minimum firmware version required for touchless provisioning (TLP) to function. If a handset is no longer supported or running an unsupported firmware version it will not be able to be TLP'd and will require the auto provisioning details to be manually entered into the handset if it is factory reset.
NOTE: Unless a handset is factory reset it will continue to function without issue and is not affected by these changes.
There is no alternate solution that enables TLP functionality on unsupported devices.
A link to the Yealink announcement can be found here
Devices No Longer Supported
SIP-T19P
SIP-T20P
SIP-T22P
SIP-T26P
SIP-T27P
SIP-T28P
SIP-T32G
SIP-T38G
SIP-T41P
SIP-T42G
SIP-T46G
SIP-T48G
SIP-T52S
SIP-T54S
CP860
Devices With Minimum Firmware Requirements
SIP-T19P_E2
SIP-T21P_E2
SIP-T23G
SIP-T27G
SIP-T29G
SIP-T40G
SIP-T40P
SIP-T41S
SIP-T42S
SIP-T46S
SIP-T48S
SIP-T53
SIP-T53W
SIP-T54W
SIP-T57W
SIP-T56A
T58A
CP920
CP960
W52P
W60B
W52H
W56H
W53HV85
W56HV85
W59RV85