How to add prepaid Visa card as payment method?

I don't think a prepaid card counts as either a credit card or a debit card because it isn't traceable though a financial agency as being billed to you personally.

See the payment types you can use and the list of stipulations at the bottom of this document:

Payment methods that you can use with your Apple ID --> https://support.apple.com/HT202631

E.g. "Make sure that the billing address for your payment method matches the billing address for your Apple ID. In some cases, you might need to call your bank or financial institution to authorize international or online purchases. You might also need to confirm that the mobile number associated with your payment method is correct."

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I can’t download games I

Why can't you download games? What happens when you try? Error message(s)? More information would help.