How do I use Express Checkout with Reference Transactions?

We require that you create a token, initiate a Billing Agreement API call, and then reference the Billing Agreement ID to initiate payment. 

To use Express Checkout with Reference Transactions, follow these steps: 

1. Set up the token using a SetExpress Checkout API request call. 
2. Initiate a CreateBillingAgreement API call.
3. Reference the Billing Agreement ID in the API response to initiate a payment using the DoReferenceTransaction API call.