curl --request POST \
  --url https://api.ctrl-hub.com/v3/operations/{operation_id}/relationships/assignees \
  --header 'Content-Type: application/vnd.api+json' \
  --header 'X-Session-Token: <api-key>' \
  --data '
{
  "data": [
    {
      "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "type": "<string>"
    }
  ]
}
'

import requests

url = "https://api.ctrl-hub.com/v3/operations/{operation_id}/relationships/assignees"

payload = { "data": [
        {
            "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
            "type": "<string>"
        }
    ] }
headers = {
    "X-Session-Token": "<api-key>",
    "Content-Type": "application/vnd.api+json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {'X-Session-Token': '<api-key>', 'Content-Type': 'application/vnd.api+json'},
  body: JSON.stringify({data: [{id: '3c90c3cc-0d44-4b50-8888-8dd25736052a', type: '<string>'}]})
};

fetch('https://api.ctrl-hub.com/v3/operations/{operation_id}/relationships/assignees', 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://api.ctrl-hub.com/v3/operations/{operation_id}/relationships/assignees",
  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([
    'data' => [
        [
                'id' => '3c90c3cc-0d44-4b50-8888-8dd25736052a',
                'type' => '<string>'
        ]
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/vnd.api+json",
    "X-Session-Token: <api-key>"
  ],
]);

$response = curl_exec($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://api.ctrl-hub.com/v3/operations/{operation_id}/relationships/assignees"

	payload := strings.NewReader("{\n  \"data\": [\n    {\n      \"id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n      \"type\": \"<string>\"\n    }\n  ]\n}")

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

	req.Header.Add("X-Session-Token", "<api-key>")
	req.Header.Add("Content-Type", "application/vnd.api+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.ctrl-hub.com/v3/operations/{operation_id}/relationships/assignees")
  .header("X-Session-Token", "<api-key>")
  .header("Content-Type", "application/vnd.api+json")
  .body("{\n  \"data\": [\n    {\n      \"id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n      \"type\": \"<string>\"\n    }\n  ]\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.ctrl-hub.com/v3/operations/{operation_id}/relationships/assignees")

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

request = Net::HTTP::Post.new(url)
request["X-Session-Token"] = '<api-key>'
request["Content-Type"] = 'application/vnd.api+json'
request.body = "{\n  \"data\": [\n    {\n      \"id\": \"3c90c3cc-0d44-4b50-8888-8dd25736052a\",\n      \"type\": \"<string>\"\n    }\n  ]\n}"

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

{
  "id": "98ca4a78-b66f-4234-9719-aaf832ee6669",
  "status": "400",
  "title": "A validation error was encountered",
  "source": {
    "parameter": "include"
  },
  "meta": {
    "resource": "wrong_value"
  }
}

{
  "id": "05fc9c8d-73b9-4697-9337-57f7a567a48f",
  "status": "401",
  "title": "You are not authorised to access this resource",
  "detail": "In order to access this resource, you need the 'admin' role.",
  "code": "AUTH.001"
}

{
  "id": "fe9d9a69-f0a7-4fdc-bb2c-176027f316c5",
  "status": "500",
  "title": "Internal Server Error",
  "detail": "An unexpected error occurred on the server."
}