There are many discussions on this forum regarding these covers and the two different rail types. I believe BAK has rails to fit either the black or silver rails - and thought the silver just came on later builds. Mine has silver and the rails that they sent me (that were correct for silver) did not fit, so they sent me a modified rail, which has a mount that I thought would work with any rail. See the photo. It may be hard to see but it has a tab that slides and then tightens from the top.
After calling BAK directly and Morrie at TFO, they both agreed that the only option for the MX4 and practically every other tonneau cover is the silver rails. The only tonneau cover that works with the black rails is the soft mopar trifold.