NVENC SDK question.

Hi all,
Can someone tell me how to avoid NV_ENC_ERR_INCOMPATIBLE_CLIENT_KEY in nvEncOpenEncodeSession ? I have 660Ti and as far as I understood from description HW NVENC will not work on this card, but according to this topic https://devtalk.nvidia.com/default/topic/518482/cuda-programming-and-performance/where-can-i-get-gtx-680-nvenc-sdk-/ the key may be granted and directly provided to encoder. I wonder if it’s true and what are the limitations of the trial version of the key ?