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You don't have to put money on your Yahoo iTunes account. All you have to do is, just add your credit card info on your Apple ID (you use your Yahoo account as Apple ID) and iTunes will use that card everytime you purchase something from the store. You can add credit credit to your Apple ID from here --> https://appleid.apple.com/signin
If you have any questions or would like any additional information, please don't hesitate to ask.
The money you put on your iCloud ID is for additional storage space only.
You can add your card on your iTunes by following the following onscreen instructions.
If you want to put prepaid money on iTunes account, then you have to buy iTunes Gift Card and redeem that Gift card on your account. You can buy gift card from here --> http://www.apple.com/shop/personalize/itunes
To redeem that gift card to your iTunes account, follow the instructions in here --> https://support.apple.com/en-in/HT201209
If this is your own Apple ID, then you only need to add your card and that card will be used only if you make purchases. If you have any questions or would like any additional information, please don't hesitate to ask.
Have you tried redeeming that gift card on iTunes account directly ? Please try the steps below
If it is added to your iTunes account, then you will see the amount under Apple ID (like $25 Credit). See sample picture here --> https://support.apple.com/library/content/dam/edam/applecare/images/en_US/ios/itunes/ios8_account_balance.png