There is several Yzyspot release now. Yzyspot 1.0.4 to 2.0.1 are based on DD-WRT kernel, Yzyspot OWT are based on Openwrt kernel.
Yzyspot 1.0.4 a 2.0.1
This firmawe are "WebFlash" kind. Your router should then have already been flashed with DD-WRT and should be activated at DD-WRT.com
Intial DD-WRT Flashing should be done with DD-WRT V24SP2 14896 (not higher) !
Once your device fully activated, you could flash it with YzySpot Firmware though the Router Web UI.
Yzyspot OWT X.X.X
This kind of firmware are tftp initial flashing kind and did not require activation key extracost. You should follow the TFTP method to flah your ubiquiti devices.
Note: Yzyspot OWT 1.0.0 did not include PPTP Server that could work with captive portal against Yzyspot 2.0.1. This feature is WIP for the next release (2.x.X)