curl --request POST \
  --url https://app.gtm-api.com/orchestration/v4/api/mass-actions/{sid}/append-items \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'Team-SID: <api-key>' \
  --data '
{
  "identities": [
    {}
  ]
}
'

import requests

url = "https://app.gtm-api.com/orchestration/v4/api/mass-actions/{sid}/append-items"

payload = { "identities": [{}] }
headers = {
    "Authorization": "Bearer <token>",
    "Team-SID": "<api-key>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {
    Authorization: 'Bearer <token>',
    'Team-SID': '<api-key>',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({identities: [{}]})
};

fetch('https://app.gtm-api.com/orchestration/v4/api/mass-actions/{sid}/append-items', 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://app.gtm-api.com/orchestration/v4/api/mass-actions/{sid}/append-items",
  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([
    'identities' => [
        [
                
        ]
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json",
    "Team-SID: <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://app.gtm-api.com/orchestration/v4/api/mass-actions/{sid}/append-items"

	payload := strings.NewReader("{\n  \"identities\": [\n    {}\n  ]\n}")

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

	req.Header.Add("Authorization", "Bearer <token>")
	req.Header.Add("Team-SID", "<api-key>")
	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://app.gtm-api.com/orchestration/v4/api/mass-actions/{sid}/append-items")
  .header("Authorization", "Bearer <token>")
  .header("Team-SID", "<api-key>")
  .header("Content-Type", "application/json")
  .body("{\n  \"identities\": [\n    {}\n  ]\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://app.gtm-api.com/orchestration/v4/api/mass-actions/{sid}/append-items")

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

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Team-SID"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"identities\": [\n    {}\n  ]\n}"

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

{
  "success": true,
  "operation": "action",
  "action": "<string>",
  "item": {
    "sid": "<string>",
    "team_sid": "<string>",
    "target_entity": "<string>",
    "plan": {},
    "total_count": 123,
    "title": "<string>",
    "schedule": {},
    "hold_till": "<string>",
    "canary_satisfied_at": "<string>",
    "started_at": "<string>",
    "settled_at": "<string>",
    "created_by": {
      "actor_sid": "<string>",
      "team_sid": "<string>",
      "permissions": {},
      "request_sid": "<string>",
      "reason": "<string>"
    },
    "deleted_by": {
      "actor_sid": "<string>",
      "team_sid": "<string>",
      "permissions": {},
      "request_sid": "<string>",
      "reason": "<string>"
    },
    "created_at": "<string>",
    "updated_at": "<string>",
    "deleted_at": "<string>"
  },
  "result": {
    "enrolled_count": 123,
    "skipped_duplicate_count": 123,
    "total_count": 123
  },
  "meta": {
    "trace_id": "<string>",
    "span_id": "<string>",
    "timestamp": "<string>",
    "duration_ms": 1,
    "debug_url": "<string>"
  }
}

{
  "success": false,
  "error": {
    "message": "<string>",
    "recoverable": true,
    "suggestion": "<string>",
    "field_errors": {},
    "blockers": [
      {
        "type": "<string>",
        "description": "<string>",
        "entity_sid": "<string>",
        "resolution": "<string>",
        "resolution_hint": "<string>",
        "count": 123
      }
    ],
    "context": {}
  },
  "meta": {
    "trace_id": "<string>",
    "span_id": "<string>",
    "timestamp": "<string>",
    "duration_ms": 1,
    "debug_url": "<string>"
  }
}

{
  "success": false,
  "error": {
    "message": "<string>",
    "recoverable": true,
    "suggestion": "<string>",
    "field_errors": {},
    "blockers": [
      {
        "type": "<string>",
        "description": "<string>",
        "entity_sid": "<string>",
        "resolution": "<string>",
        "resolution_hint": "<string>",
        "count": 123
      }
    ],
    "context": {}
  },
  "meta": {
    "trace_id": "<string>",
    "span_id": "<string>",
    "timestamp": "<string>",
    "duration_ms": 1,
    "debug_url": "<string>"
  }
}