The transaction speed setting determines how quickly an invoice payment is considered to be "confirmed," which would be the status at which you would fulfill and complete the order.
High speed (High Risk):
Medium speed (Moderate Risk):
Low speed (Low Risk):
For more information on these confirmation states, please review the "Invoice States" section of our technical documentation: https://bitpay.com/docs/invoice-states
NOTE: Regardless of the transaction speed settings, a fully paid invoice is credited to your merchant account after the transaction has accrued six confirmations on the bitcoin network.