Hi Caden 101,
It sounds like you do not have a payment method to enter after signing into the iTunes Store for the first time. According to the following article for an existing Apple ID you must enter a payment method:
Create an iTunes Store, App Store, or iBooks Store account without a credit card or other payment method
If you've already created your Apple ID, you'll need to add a payment method when you first use it to sign in to the iTunes Store, App Store, or iBooks Store. But you can optionally remove the payment methodafter you sign in to the store. You won't be asked for a payment method again until you make your first purchase.
You do have the option of creating a new Apple ID and when you are setting that up you have the option to select None for your payment method using the section of the above article named "If you don't have an Apple ID"
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