When buying drugs, or drug memorabilia, dealers might send photos or text, Snapchat stories ect of their merchandise telling you to "Tap in." This just mean to claim what you want.
Northern California slang , more specificaly , MOZZY SLANG 916, OAK PARK , fuck wit us!! TAP INWARDLY! That means breathe on me , call me , hit me. You got my line , utilize that mothafucka