How you want to obtain payment. Required Authorization indicates that this payment is a basic authorization subject to settlement with PayPal Authorization and Capture. Order indicates that this payment is is an order authorization subject to settlement with PayPal Authorization and Capture. Sale indicates that this is a final sale for which you are requesting payment. IMPORTANT: You cannot set PaymentAction to Sale on SetExpressCheckoutRequest and then change PaymentAction to Authorization on the final Express Checkout API, DoExpressCheckoutPaymentRequest. Character length and limit: Up to 13 single-byte alphabetic characters