Option 1: their account was created before a certain period of time, they have tried to apply a promo code, however, the promo is applicable for new accounts only.
Option 2: they have signed via your link, and it is just a matter of time until our team reviews their account (to ensure that all criteria are met). Then after a free share will be allocated.
The best way to have the matter resolved is to ask them to reach us at info@trading212.com, and we will assist them further.