In reply to John.

The SSN number is required since they are debiting your checking account presumably without the ability to verify available funds. This is similar to store debit cards like Target RedCard debit or Safeway FastForward. With debit or POS transactions, the network (such as Visa, Interlink or Star) should validate available funds, but of course that comes with interchange fees to the merchant. But apparently even that's too much so they want to offer a channel that bypasses all of this. Oh and we'll get a coupon or discount for doing so.