How do I use keys instead of money to gift a friend backpack.tf premium?

[High Medic]

I want to gift a friend backpack.tf premium, although it only seems to ask me to input my card info and pay money instead of using keys to do so in the same way that I had done so when I got myself premium through keys that I gave. I also don't want to trade said person the keys either, as I want it to be a surprise.

 

Any help is very much appreciated. Thank you for your time! 

[Zeus_Junior]

Can’t gift with items

[High Medic]

Thank you!