Nostalrius Begins - Quality wow vanilla realm (1.12)

I just downloaded the game, and was able to log in to the website, but am unable to log in to the game itself.

Make sure you created an account on the Website (not the forums) since a forum account isn't equal to the ingame account.

https://en.nostalrius.org/register

If you did that and it doesn't work, make sure your realmlist is 100% correct.

Also make sure your client is 1.12 and you're starting the wow.exe (not the launcher)