Following the EC documentation, copy the transaction structures, staging and unstaging functions we'll need:

• SetExpressCheckout **
• DoExpressCheckoutPayment
  • https://developer.paypal.com/docs/classic/api/merchant/DoExpressCheckoutPayment_API_Operation_NVP/

• Recurring variants of the above. (MerchantInitiatedBillingSingleAgreement)

L_BILLINGAGREEMENTDESCRIPTION0 should summarize billing agreement terms, for recurring subscriptions.