In Drupal Commerce, carts do not have order numbers. Order numbers are not set until checkout completion, when the order is placed. If the order type has been configured with a number pattern, that pattern is used to generate the order number; otherwise the order entity ID is used. As a result, when a credit card payment is added during checkout, the cart/order may not have its final Order Number yet. For some payment gateways, this is fine--only the order entity ID is needed.