1. 首先，我们需要使用HTTP请求的方式调用Business Central API的Endpoint，以关闭销售退货订单。以下是使用C#代码示例：

using System;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;

namespace CloseSalesReturnOrder
{
    class Program
    {
        static async Task Main(string[] args)
        {
            using (var httpClient = new HttpClient())
            {
                // Replace with your API Endpoint URL
                var url = "https://api.businesscentral.dynamics.com/v2.0/{your-tenant}/api/v1.0/companies({your-company})/salesReturnOrders({your-order})/close";

                // Replace with your API Authorization Token
                var authToken = "Your-API-Authorization-Token";

                httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", authToken);

                var requestBody = new StringContent("{ }", System.Text.Encoding.UTF8, "application/json");

                var response = await httpClient.PostAsync(url, requestBody);

                if(response.StatusCode == System.Net.HttpStatusCode.OK)
                {
                    Console.WriteLine("Sales Return Order has been successfully closed.");
                }
                else
                {
                    Console.WriteLine("Failed to close Sales Return Order.");
                }
            }
        }
    }
}

2. 然后，我们需要使用上述代码中的URL字符串和Authorization Token来替换URL中的{your-tenant}、{your-company}和{your-order}。

3. 最后，我们可以执行代码并检查控制台的输出，以确认销售退货订单是否已经成功关闭。