PayPal API Guide for Merchant Backoffice Applications

Use Chilkat to collect a payment, ship an order, refund a customer, or reconcile the day’s activity from the merchant’s own backoffice application.

Choose the payment flow that fits the sale. A reusable Payment Link works for a service sold at a catalog price. An invoice bills a named customer for specific work. An order connects a buyer’s checkout to the authorization and capture that your staff can look up later.

C# walkthrough: read an invoice

Suppose a customer asks how much they still owe. After obtaining a sandbox token, look up the PayPal invoice ID on their local billing record. The following C# code uses Chilkat.Http to retrieve the invoice and Chilkat.JsonObject to read its outstanding balance. The linked examples use Chilkat 11.0.0 or later.

// accessToken comes from merchant credentials; invoiceId comes from the billing record.
var http = new Chilkat.Http();
http.AuthToken = accessToken;
http.SetUrlVar("id", invoiceId);
var response = new Chilkat.HttpResponse();
if (!http.HttpNoBody("GET", "https://api-m.sandbox.paypal.com/v2/invoicing/invoices/{$id}", response)) {
    Console.WriteLine(http.LastErrorText);
    return;
}
var invoice = new Chilkat.JsonObject();
if (response.StatusCode != 200) {
    invoice.Load(response.BodyStr);
    Console.WriteLine("HTTP " + response.StatusCode + "  PayPal debug ID: " + invoice.StringOf("debug_id"));
    return;
}
if (!invoice.Load(response.BodyStr)) {
    Console.WriteLine("Expected invoice JSON.");
    return;
}
Console.WriteLine(invoice.StringOf("detail.invoice_number") + "  " + invoice.StringOf("status"));
Console.WriteLine("Balance due: " + invoice.StringOf("due_amount.value") + " " +
                  invoice.StringOf("due_amount.currency_code"));

HttpNoBody reports whether an HTTP response arrived. Check the HTTP status before using the JSON. For an operation that writes data and supports PayPal-Request-Id, such as a capture or refund, save a unique request ID with the operation before sending it. If the outcome is uncertain, retry the same request with the saved ID within PayPal’s retention period. PayPal’s retry guidance.