Welcome to the HP Support Forum! I hope you enjoy your experience here. ヾ(⌐■_■)ノ♪
I see that you're curious about making an Instant Ink payment. I have a simple answer: don't. You can only pay for the service as an active subscriber using a debit or credit card (Master Card, Amex, Visa, Discover).
Your bank can issue to you a "prepaid credit card" -- you transfer money onto the card, and then use that credit-card to make an online payment. Some people who are paranoid about using a credit-card over the Internet have a "low-limit" prepaid credit card that they use for all their purchases.