Best answer by Tim_OVO
There's a good few reasons for why this might be happening,
My advice would be to get your friend to sign up directly with OVO online here.
At the same time, send over an email to firstname.lastname@example.org, or better yet, a Facebook PM here
Mention your name, email address and full address, and the name and email address of the friend who signed up. Then when the friend is on supply, we can sort out those vouchers for you!