How Square Moves Cash
Jon White (via Hacker News):
Once you do this, Square will send you an e-mail that asks you to enter your debit card info, and you are done. Cash sent. On the receiving side, you also get an e-mail asking for your debit card, and nothing more. There are no bank account numbers involved, how can they do this? The answer deceptively simple: they issue a refund to your debit card for the amount you are sent.
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Now, you can use Square Cash directly with a bank account, but only for receiving money, since the two-step ACH verification process is only needed to make withdrawals from an account. A debit card is still required to send cash.
