Add Reversal API to PaymentsClient

[nicklmiller]

Environment

• Checkout SDK version: 4.3.4

Description

Checkout has a new Reversals API endpoint for Payments. It is a helper API that chooses between Refund and Void based on the payment. It would be great if it could get added to this SDK.

Proposed Solution

Add a ReversePayment method to PaymentsClient.