Pretty sure the UAP-AC-LITE only supports passive PoE native. It "supports" 802.3af through the use of a proprietary Ubnt injector.
It does support 802.3 now, but you need a unit that specifically supports it. The Lite didn't always support it, so unless the box has a sticker on it indicating compatibility, then it won't work.
MRCUR | CMNO #12