curl --request POST \
  --url https://cloudapi.mailercloud.com/v1/campaign/testmail/{id} \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: <content-type>' \
  --data '
{
  "email": "sender@yourdomain.com",
  "testmail_group": "group_name/group_id"
}
'

import requests

url = "https://cloudapi.mailercloud.com/v1/campaign/testmail/{id}"

payload = {
    "email": "sender@yourdomain.com",
    "testmail_group": "group_name/group_id"
}
headers = {
    "Content-Type": "<content-type>",
    "Authorization": "<api-key>"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {'Content-Type': '<content-type>', Authorization: '<api-key>'},
  body: JSON.stringify({email: 'sender@yourdomain.com', testmail_group: 'group_name/group_id'})
};

fetch('https://cloudapi.mailercloud.com/v1/campaign/testmail/{id}', 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://cloudapi.mailercloud.com/v1/campaign/testmail/{id}",
  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([
    'email' => 'sender@yourdomain.com',
    'testmail_group' => 'group_name/group_id'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: <api-key>",
    "Content-Type: <content-type>"
  ],
]);

$response = curl_exec($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://cloudapi.mailercloud.com/v1/campaign/testmail/{id}"

	payload := strings.NewReader("{\n  \"email\": \"sender@yourdomain.com\",\n  \"testmail_group\": \"group_name/group_id\"\n}")

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

	req.Header.Add("Content-Type", "<content-type>")
	req.Header.Add("Authorization", "<api-key>")

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

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

	fmt.Println(string(body))

}

{
  "message": "Test mail was successfully sent"
}

{
  "errors": [
    {
      "field": "email",
      "message": "Email must be a valid email address"
    }
  ]
}

{
  "errors": [
    {
      "field": "",
      "message": "Authorization failed"
    }
  ]
}

{
  "error": {
    "field": "id",
    "message": "Record not found with the given Id"
  }
}