You have to create a new user on the Wii U. You can't link it to an existing user.
#I get an error when trying to put it in
humble spruce
granite coral
You should be asked to link an nnid after making a new user, but it will actually be your pnid that you enter. None of the actual text is changed during setup but you should enter your pnid info regardless. Just make sure you are connected to pretendo servers via the plugin