So to understand you better, You have a IP camera either POE or Non POE that has face detection that has face detection enabled in the camera that is connected to your NVR, The NVR has the Ai tab on the main menu where you click on the Ai and go to Smart Plan, Then Pick the camera channel with FD and there is no option enabled there for Face Detection? While I do have that NVR mine pre dates and is watered down version with no Ai, So does yours have the Ai with Face Detection as an option in the Smart Plan? If you don't have an Enhanced AI NVR like my 4216E-AI and my 4216-E1 that offers the built in option of AI for a select few channels then you would need a camera that has the option and might have the NVR model that would need the camera have the AI option enabled before Ai would show in the list.. Can I see a picture of your main WebUI menu might look like one of my 2 here..