The first thing we'd suggest is to have your friend check their spam / junk folder in their emails. These are automated emails and sometimes email clients will push them straight into the junk folder.
There could also be a couple of other reasons why including if you have...
- sent more than 3 different refer a friend codes in a month.
- Used multiple different email addresses to send refer a friend codes.
- Have tried to refer yourself.
- If you have tried to refer a person with the same first name and last name multiple times.
- Have tried to refer a person with the same sirname multiple times
- Have tried to refer people in the same house as you
If you have done any of the above your account will be placed on hold and you should try again after a month.