For complete examples and details for your finalized Express Checkout call, go to PayPal Express Checkout Integration.
Why did I get API error code 10411?
How do I set up and process an API call using the Payflow .NET SDK?
Do I need to use PayPal SDKs to call PayPal APIs?
Why did I get API error code 10423?
How do I obtain the buyer’s shipping address using Express Checkout?