using RestSharp;


var options = new RestClientOptions("https://api.sandbox.{id}.gr4vy.app/transactions/{transaction_id}/refunds/all");
var client = new RestClient(options);
var request = new RestRequest("");
request.AddHeader("Authorization", "Bearer <token>");
request.AddJsonBody("{\n  \"reason\": \"Refund due to user request\"\n}", false);
var response = await client.PostAsync(request);

Console.WriteLine("{0}", response.Content);

package main

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

func main() {

	url := "https://api.sandbox.{id}.gr4vy.app/transactions/{transaction_id}/refunds/all"

	payload := strings.NewReader("{\n  \"reason\": \"Refund due to user request\"\n}")

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

	req.Header.Add("Authorization", "Bearer <token>")
	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://api.sandbox.{id}.gr4vy.app/transactions/{transaction_id}/refunds/all")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"reason\": \"Refund due to user request\"\n}")
  .asString();

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.sandbox.{id}.gr4vy.app/transactions/{transaction_id}/refunds/all",
  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([
    'reason' => 'Refund due to user request'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json"
  ],
]);

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

curl_close($curl);

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

import requests

url = "https://api.sandbox.{id}.gr4vy.app/transactions/{transaction_id}/refunds/all"

payload = { "reason": "Refund due to user request" }
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({reason: 'Refund due to user request'})
};

fetch('https://api.sandbox.{id}.gr4vy.app/transactions/{transaction_id}/refunds/all', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

curl --request POST \
  --url https://api.sandbox.{id}.gr4vy.app/transactions/{transaction_id}/refunds/all \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "reason": "Refund due to user request"
}
'

{
  "items": [
    {
      "type": "refund",
      "id": "8724fd24-5489-4a5d-90fd-0604df7d3b83",
      "transaction_id": "fe26475d-ec3e-4884-9553-f7356683f7f9",
      "payment_service_refund_id": "refund_xYqd43gySMtori",
      "status": "processing",
      "currency": "USD",
      "amount": 1299,
      "reason": "Refund due to user request",
      "created_at": "2013-07-16T19:23:00.000+00:00",
      "updated_at": "2013-07-16T19:23:00.000+00:00",
      "target_type": "payment-method",
      "target_id": "c23ea83f-1b1c-4584-a0e8-78ef8c041949",
      "external_identifier": "refund-789123",
      "reconciliation_id": "7jZXl4gBUNl0CnaLEnfXbt",
      "transaction_external_identifier": "transaction-789123",
      "transaction_reconciliation_id": "7jZXl4gBUNl0CnaLEnfXbt"
    }
  ],
  "limit": 1,
  "next_cursor": "ZXhhbXBsZTE",
  "previous_cursor": null
}

{
  "type": "error",
  "code": "bad_request",
  "status": 400,
  "message": "Missing '****' field",
  "details": [
    {
      "location": "body",
      "type": "value_error.missing",
      "pointer": "/payment_method/number",
      "message": "field required"
    }
  ]
}

{
  "type": "error",
  "code": "unauthorized",
  "status": 401,
  "message": "No valid API authentication found",
  "details": []
}

{
  "type": "error",
  "code": "not_found",
  "status": 404,
  "message": "The resource could not be found",
  "details": []
}