curl --request POST \
  --url https://api.hubapi.com/crm/v3/associations/{fromObjectType}/{toObjectType}/batch/create \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "inputs": [
    {
      "from": {
        "id": "53628"
      },
      "to": {
        "id": "12726"
      },
      "type": "contact_to_company"
    }
  ]
}
'

import requests

url = "https://api.hubapi.com/crm/v3/associations/{fromObjectType}/{toObjectType}/batch/create"

payload = { "inputs": [
        {
            "from": { "id": "53628" },
            "to": { "id": "12726" },
            "type": "contact_to_company"
        }
    ] }
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({inputs: [{from: {id: '53628'}, to: {id: '12726'}, type: 'contact_to_company'}]})
};

fetch('https://api.hubapi.com/crm/v3/associations/{fromObjectType}/{toObjectType}/batch/create', 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.hubapi.com/crm/v3/associations/{fromObjectType}/{toObjectType}/batch/create",
  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([
    'inputs' => [
        [
                'from' => [
                                'id' => '53628'
                ],
                'to' => [
                                'id' => '12726'
                ],
                'type' => 'contact_to_company'
        ]
    ]
  ]),
  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;
}

package main

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

func main() {

	url := "https://api.hubapi.com/crm/v3/associations/{fromObjectType}/{toObjectType}/batch/create"

	payload := strings.NewReader("{\n  \"inputs\": [\n    {\n      \"from\": {\n        \"id\": \"53628\"\n      },\n      \"to\": {\n        \"id\": \"12726\"\n      },\n      \"type\": \"contact_to_company\"\n    }\n  ]\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.hubapi.com/crm/v3/associations/{fromObjectType}/{toObjectType}/batch/create")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"inputs\": [\n    {\n      \"from\": {\n        \"id\": \"53628\"\n      },\n      \"to\": {\n        \"id\": \"12726\"\n      },\n      \"type\": \"contact_to_company\"\n    }\n  ]\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.hubapi.com/crm/v3/associations/{fromObjectType}/{toObjectType}/batch/create")

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

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"inputs\": [\n    {\n      \"from\": {\n        \"id\": \"53628\"\n      },\n      \"to\": {\n        \"id\": \"12726\"\n      },\n      \"type\": \"contact_to_company\"\n    }\n  ]\n}"

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

{
  "completedAt": "2023-11-07T05:31:56Z",
  "results": [
    {
      "from": {
        "id": "53628"
      },
      "to": {
        "id": "12726"
      },
      "type": "contact_to_company"
    }
  ],
  "startedAt": "2023-11-07T05:31:56Z",
  "links": {},
  "requestedAt": "2023-11-07T05:31:56Z"
}

{
  "completedAt": "2023-11-07T05:31:56Z",
  "results": [
    {
      "from": {
        "id": "53628"
      },
      "to": {
        "id": "12726"
      },
      "type": "contact_to_company"
    }
  ],
  "startedAt": "2023-11-07T05:31:56Z",
  "errors": [
    {
      "category": "<string>",
      "context": {},
      "errors": [
        {
          "message": "<string>",
          "code": "<string>",
          "context": "{missingScopes=[scope1, scope2]}",
          "in": "<string>",
          "subCategory": "<string>"
        }
      ],
      "links": {},
      "message": "<string>",
      "status": "<string>",
      "id": "<string>",
      "subCategory": {}
    }
  ],
  "links": {},
  "numErrors": 123,
  "requestedAt": "2023-11-07T05:31:56Z"
}

{
  "message": "Invalid input (details will vary based on the error)",
  "correlationId": "aeb5f871-7f07-4993-9211-075dc63e7cbf",
  "category": "VALIDATION_ERROR",
  "links": {
    "knowledge-base": "https://www.hubspot.com/products/service/knowledge-base"
  }
}