Prepaid cards aren't supported. Sorry for the inconvenience!
You'll need a transactional bank account (one that allows for both deposits and withdrawals) to link to your Square account. This is because, as a seller, you'll need to support refunds and chargebacks.
This article has more info: https://squareup.com/help/us/en/article/3896-link-and-edit-your-bank-account
