Additional information: This spell became purchaseable for me as soon as I reached Tier 3 (level 20) Incantation, although my Invocation was only level 15. I was able to purchase it for only 170 gold, but have not been able to add it to my deck.
@silentseer It can take up to 24 hours to get the codes/invitations, and since the company is in Denmark they are often on a different time zone than others. I would expect to see the emails sent out tomorrow or Sunday at the latest, since it's a weekend. Check out the FAQ for more details!