Paypal is available as a payment method for the Shopify subscription if your store is located in any country other than the United States. If you are in the United States, then the only supported payment method available is a valid credit card.
If you're in the United States, then I would recommend contacting your bank to determine if you can enable online purchases for your card. Alternatively, they may be able to offer a credit card that you can use for online purchases. If not, you can also choose to use a friend's or family member's card to place on the account then transfer them the funds at a later time.
Trevor | Community Moderator @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog