curl --request POST \
  --url https://api.hubapi.com/crm/v3/objects/0-3 \
  --header 'Content-Type: application/json' \
  --data '
{
  "associations": [
    {
      "to": {
        "id": "<string>"
      },
      "types": [
        {
          "associationTypeId": 123
        }
      ]
    }
  ],
  "properties": {}
}
'

import requests

url = "https://api.hubapi.com/crm/v3/objects/0-3"

payload = {
    "associations": [
        {
            "to": { "id": "<string>" },
            "types": [{ "associationTypeId": 123 }]
        }
    ],
    "properties": {}
}
headers = {"Content-Type": "application/json"}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({
    associations: [{to: {id: '<string>'}, types: [{associationTypeId: 123}]}],
    properties: {}
  })
};

fetch('https://api.hubapi.com/crm/v3/objects/0-3', 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/objects/0-3",
  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([
    'associations' => [
        [
                'to' => [
                                'id' => '<string>'
                ],
                'types' => [
                                [
                                                                'associationTypeId' => 123
                                ]
                ]
        ]
    ],
    'properties' => [
        
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "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/objects/0-3"

	payload := strings.NewReader("{\n  \"associations\": [\n    {\n      \"to\": {\n        \"id\": \"<string>\"\n      },\n      \"types\": [\n        {\n          \"associationTypeId\": 123\n        }\n      ]\n    }\n  ],\n  \"properties\": {}\n}")

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

	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/objects/0-3")
  .header("Content-Type", "application/json")
  .body("{\n  \"associations\": [\n    {\n      \"to\": {\n        \"id\": \"<string>\"\n      },\n      \"types\": [\n        {\n          \"associationTypeId\": 123\n        }\n      ]\n    }\n  ],\n  \"properties\": {}\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.hubapi.com/crm/v3/objects/0-3")

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

request = Net::HTTP::Post.new(url)
request["Content-Type"] = 'application/json'
request.body = "{\n  \"associations\": [\n    {\n      \"to\": {\n        \"id\": \"<string>\"\n      },\n      \"types\": [\n        {\n          \"associationTypeId\": 123\n        }\n      ]\n    }\n  ],\n  \"properties\": {}\n}"

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

{
  "archived": false,
  "createdAt": "2019-10-30T03:30:17.883Z",
  "id": "512",
  "properties": {
    "property_checkbox": "false",
    "property_date": "1572480000000",
    "property_dropdown": "choice_b",
    "property_multiple_checkboxes": "chocolate;strawberry",
    "property_number": "17",
    "property_radio": "option_1",
    "property_string": "value"
  },
  "updatedAt": "2019-12-07T16:50:06.678Z"
}

{
  "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"
  }
}