Nov 25, 2017, 10:3211/25/17
@SAB_Vanier (3 December, 2017, 3:40 PM UTC):
I've never sent or received one of those emails before, but this is my speculation:
Plarium sends their email, which contains THREE (3) links: One for the invitation, one for Plarium's site, and one DIRECTLY to the game.
Your friend may have clicked on the link DIRECTLY to the game, instead of the invitation.
I may be wrong, but that's my speculation; Regardless, there's nothing we can do, since your friend has already created an account.