So I play this game on my iPod, Love Live: School Idol Festival. Within this game you can buy currency called love gems. I want to buy 50 of them, but need to add $10 more credit to my account to do it. I don't want to spend around $30 from the credit/debit/not a gift card. I already have $20 worth of credit on my account. It's just the $10 more I need. Is it possible to put $10 of credit into my account from a credit/debit/not a gift card? I've looked but the cheapest App Store card I can find is $25. I don't need $25. And I don't want to spend $15 unnecessarily. Or if I buy the gems can I charge the remaining to said credit/debit/not a gift card? It's hooked up to a PayPal account, could I add $10 through that? Please help me for I am deep in idol hell and am on a time limit as to when I can figure this out for what I want to spend the gems on if/when I buy them.
Here's what you can do: you can have a gift card credit on your account as well as a linked credit card. Here's what you can't do: you can't only add $10 from a credit card to your iTunes account. But if you have a credit on your account now, and you link a credit card to your account, it will use all the remaining credit from the gift card first, then charge the remaining amount to your credit card.
I use the Wallet/Passbook to add funds to my account at Apple Retail stores. They take all sorts of payment there, but you'd need to go to the store physically to pay.
I'm not aware of a way to load the account yourself using the iOS app or online. There also are $15 and $10 cards you can buy online - you need to trust that the vendor will email you a valid code - but I've not had issues when I use a major retailer like Target to make an online purchase.
You could also send a friend to the Apple Store to buy a blank card with the custom amount you desire - they have blank cards for that purpose.
Online sales from Apple doesn't seem to cary the custom amount cards so you've got lots of options to not over spend if you can take advantage of one of them.