curl --request POST \
  --url https://{domain}/api/DeclineCallback \
  --header 'Content-Type: application/json' \
  --data '
{
  "MachineId": 71234996,
  "HwSerial": "0434334921100366",
  "SparkTransactionId": "12c7cec2-c690-4425-9a1f-db0db60e2d8c",
  "Status": {
    "Verdict": "Declined",
    "ErrorCode": 44,
    "ErrorDescription": "Timeout on POS Device"
  }
}
'

import requests

url = "https://{domain}/api/DeclineCallback"

payload = {
    "MachineId": 71234996,
    "HwSerial": "0434334921100366",
    "SparkTransactionId": "12c7cec2-c690-4425-9a1f-db0db60e2d8c",
    "Status": {
        "Verdict": "Declined",
        "ErrorCode": 44,
        "ErrorDescription": "Timeout on POS Device"
    }
}
headers = {"Content-Type": "application/json"}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({
    MachineId: 71234996,
    HwSerial: '0434334921100366',
    SparkTransactionId: '12c7cec2-c690-4425-9a1f-db0db60e2d8c',
    Status: {Verdict: 'Declined', ErrorCode: 44, ErrorDescription: 'Timeout on POS Device'}
  })
};

fetch('https://{domain}/api/DeclineCallback', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://{domain}/api/DeclineCallback",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'MachineId' => 71234996,
    'HwSerial' => '0434334921100366',
    'SparkTransactionId' => '12c7cec2-c690-4425-9a1f-db0db60e2d8c',
    'Status' => [
        'Verdict' => 'Declined',
        'ErrorCode' => 44,
        'ErrorDescription' => 'Timeout on POS Device'
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://{domain}/api/DeclineCallback"

	payload := strings.NewReader("{\n  \"MachineId\": 71234996,\n  \"HwSerial\": \"0434334921100366\",\n  \"SparkTransactionId\": \"12c7cec2-c690-4425-9a1f-db0db60e2d8c\",\n  \"Status\": {\n    \"Verdict\": \"Declined\",\n    \"ErrorCode\": 44,\n    \"ErrorDescription\": \"Timeout on POS Device\"\n  }\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://{domain}/api/DeclineCallback")
  .header("Content-Type", "application/json")
  .body("{\n  \"MachineId\": 71234996,\n  \"HwSerial\": \"0434334921100366\",\n  \"SparkTransactionId\": \"12c7cec2-c690-4425-9a1f-db0db60e2d8c\",\n  \"Status\": {\n    \"Verdict\": \"Declined\",\n    \"ErrorCode\": 44,\n    \"ErrorDescription\": \"Timeout on POS Device\"\n  }\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://{domain}/api/DeclineCallback")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Content-Type"] = 'application/json'
request.body = "{\n  \"MachineId\": 71234996,\n  \"HwSerial\": \"0434334921100366\",\n  \"SparkTransactionId\": \"12c7cec2-c690-4425-9a1f-db0db60e2d8c\",\n  \"Status\": {\n    \"Verdict\": \"Declined\",\n    \"ErrorCode\": 44,\n    \"ErrorDescription\": \"Timeout on POS Device\"\n  }\n}"

response = http.request(request)
puts response.read_body

{
  "SparkTransactionId": "12c7cec2-c690-4425-9a1f-db0db60e2d8c",
  "Status": {
    "Verdict": "Declined",
    "ErrorCode": 44,
    "ErrorDescription": "Timeout on POS Device"
  }
}