I can’t buy stuff of my Apple ID balance

Hi I wanted to buy robux today so I tried to use the rest of my money on my balance in my Apple ID.Last time I bought something off the £15 itunes card was a year ago.

I wanted to purchase 800 robux which costs £9.99.

But when I pressed purchase, it said I had to provide billing info.

Then it directed me to this.I don’t want to pay with card because I don’t have one.I wanted to pay with the apple iTunes card as I only bought that for robux.Also,I would probably get told off if I don’t use the all the money on the card as my parents are strict on money.Apple iTunes card isn’t an option to pay for the robux when I was going to buy it.When I first bought the card,I had bought something for £3.96 on my old account on Roblox

As you can see on my mums account,I have £11.04 and I can buy the robux.Also, it didn’t have a sign where I could use it to pay for the robux.

However when I pressed the add funds button,it said I had £0 in my balance :(

I don’t want to waste the money I had spent on the card (so that I could get Robux) so I want to use it quickly as my friends are also in the game.

I don’t know why this isn’t working (hopefully my mums Apple ID isn’t hacked). 🤞