Mastery Skills

[lmaoball]

Currently level 20 Blackguard, I've put 6 mastery points into the "Path of Malice," 5 into climbing the mastery ranks and put 1 into the actual ability of "Enraged Beating." Now, it never appeared in my abilities tab. I kept questing and eventually ran into the RVR area in Shadowlands. It bumps your rank up to 48 and the ability appeared in my hotbar, along with the fact that I could use said ability. Eventually I left to continue questing, but the ability is no longer usable. When i attempt to use it, it says something along the lines of "your level is not high enough." Wondering what this is all about. Thanks