I've been trying to log into the game with my older account (which I created during MoP) and now that I'm trying to play on Legion, it just won't let me log in. It says "We couldn't Log you in with what you just entered. Please try again (BLZ51900003)"
I've researched this particular error code and found it might be because I need to activate Legion login, yet there is no option to do so in my account. How do I fix this?