CreatePayment endpoint of Square API

Questions
2

You’re on the right track by looking at the Payments API. I think the part that you’re missing is that the source_id is where you would insert a Card Nonce (this is the one-time use token to refer to a customer’s card details).

Using API Explorer, you could see that an example would look like this:

var amountMoney = new Money.Builder()
  .Amount(100L)
  .Currency("USD")
  .Build();

var body = new CreatePaymentRequest.Builder(
    sourceId: "cnon:card-nonce-ok",
    idempotencyKey: "89831522-606e-49e1-aafb-17deaeb37795",
    amountMoney: amountMoney)
  .Build();

try
{
  var result = await client.PaymentsApi.CreatePaymentAsync(body: body);
}
catch (ApiException e)
{
  Console.WriteLine("Failed to make the request");
  Console.WriteLine($"Response Code: {e.ResponseCode}");
  Console.WriteLine($"Exception: {e.Message}");
}

The cnon:card-nonce-ok is a test value to use in Sandbox, that is intended to stand in place of an actual nonce that you would normally get from your front-end.

You’ll want to work through the Payment Form guide to get your front-end setup to accept credit card payments (assuming you’re building a web app).

You can also find examples in the GitHub docs for the DotNet (C#) SDK to see how to build your requests.

At a very basic level, the flow should follow:

Front-end (either mobile or web) to securely capture card details => Post nonce/token to backend for process => Make call to Square APIs to process nonce/token

For the final step, you can see in our docs the various ways you can process a payment.