The version "286" likely refers to the older firmware branch . However, Yealink has released much newer major versions (such as version 2.73, and later major revisions like version 72.x or 77.x depending on the hardware revision).
Disable Bluetooth on your phone so no calls interrupt the process. rt6 firmware 286 download upd
Ensure only the firmware files are in the root directory. Remove hidden system folders like "System Volume Information". The version "286" likely refers to the older firmware branch