Nostalrius Begins - Quality wow vanilla realm (1.12)

I want to install a coordinates addon, like Cartographer, but i cant.
I download and unzip the addon, and drag it in the AddOn folder in Interface.
But then nothing happens, there's no "addon" button in the character selection screen, even when i download other addons.
Why does it do that, please help.

The folder should be "AddOns," not "AddOn." Verify it has an "s" on the end, so it should be:
World of Warcraft Classic\Interface\AddOns

yeah it's called AddOns no problem