iTunes credit for a special offer for premium

[Nickykittyyy]

So I have about $72.00 on iTunes, and Spotify has an awesome offer for premium that's 99 cents for 3 months and then only 9.99 afterwards, and I want to use my iTunes credit to get it but when I try to do so on the app, it only allows me to use it on the normal Spotify subscription which is 13.00 per month which is what I don't want. How can I use my iTunes credit to get that specific offer on Spotify premium? Help PLEASE!