Pixhawk Not getting RTK

I have a pixkawk Radiolink - I cannot get the RTK working .Can someone please give me some tips to try . I verified the gps on Skystars h7HD and it works fine - basically there make be something I am missing to get the RTK on my Radiolink Px4 set up . Any advise will be appreciated .

does the pixhawk 4 with with RTK ?