if the HTTP API docs don't spell it out, you might do some packet captures while navigating the
the ANPR data in the browser interface to determine the http that needs to be used...
but from reading the user manual linked above, it looks like the cam can only record annotated images of identified traffic.
it does not appear to keep any sort of database of 'seen' plates. i think that may need to be done externally...
Have you tried Hikvision technical support?
As far as I can see - the API for this specific smart capability isn't published, unlike some of the earlier ones.
you will get a record of saved images of plates but as mentioned it is not going to database "seen" plates. with these cameras detection does not mean recognition. for example the facial detection feature will know when it sees a face but will not recognize previous detected faces. all you get is a library of images.