curl --request POST \
  --url https://api.hubapi.com/crm-object-schemas/v3/schemas \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "associatedObjects": [
    "CONTACT"
  ],
  "labels": {
    "plural": "My objects",
    "singular": "My object"
  },
  "metaType": "PORTAL_SPECIFIC",
  "name": "my_object",
  "primaryDisplayProperty": "my_object_property",
  "properties": [
    {
      "isPrimaryDisplayLabel": true,
      "label": "My object property",
      "name": "my_object_property"
    }
  ],
  "requiredProperties": [
    "my_object_property"
  ]
}
'

import requests

url = "https://api.hubapi.com/crm-object-schemas/v3/schemas"

payload = {
    "associatedObjects": ["CONTACT"],
    "labels": {
        "plural": "My objects",
        "singular": "My object"
    },
    "metaType": "PORTAL_SPECIFIC",
    "name": "my_object",
    "primaryDisplayProperty": "my_object_property",
    "properties": [
        {
            "isPrimaryDisplayLabel": True,
            "label": "My object property",
            "name": "my_object_property"
        }
    ],
    "requiredProperties": ["my_object_property"]
}
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({
    associatedObjects: ['CONTACT'],
    labels: {plural: 'My objects', singular: 'My object'},
    metaType: 'PORTAL_SPECIFIC',
    name: 'my_object',
    primaryDisplayProperty: 'my_object_property',
    properties: [
      {
        isPrimaryDisplayLabel: true,
        label: 'My object property',
        name: 'my_object_property'
      }
    ],
    requiredProperties: ['my_object_property']
  })
};

fetch('https://api.hubapi.com/crm-object-schemas/v3/schemas', 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-object-schemas/v3/schemas",
  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([
    'associatedObjects' => [
        'CONTACT'
    ],
    'labels' => [
        'plural' => 'My objects',
        'singular' => 'My object'
    ],
    'metaType' => 'PORTAL_SPECIFIC',
    'name' => 'my_object',
    'primaryDisplayProperty' => 'my_object_property',
    'properties' => [
        [
                'isPrimaryDisplayLabel' => true,
                'label' => 'My object property',
                'name' => 'my_object_property'
        ]
    ],
    'requiredProperties' => [
        'my_object_property'
    ]
  ]),
  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-object-schemas/v3/schemas"

	payload := strings.NewReader("{\n  \"associatedObjects\": [\n    \"CONTACT\"\n  ],\n  \"labels\": {\n    \"plural\": \"My objects\",\n    \"singular\": \"My object\"\n  },\n  \"metaType\": \"PORTAL_SPECIFIC\",\n  \"name\": \"my_object\",\n  \"primaryDisplayProperty\": \"my_object_property\",\n  \"properties\": [\n    {\n      \"isPrimaryDisplayLabel\": true,\n      \"label\": \"My object property\",\n      \"name\": \"my_object_property\"\n    }\n  ],\n  \"requiredProperties\": [\n    \"my_object_property\"\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-object-schemas/v3/schemas")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"associatedObjects\": [\n    \"CONTACT\"\n  ],\n  \"labels\": {\n    \"plural\": \"My objects\",\n    \"singular\": \"My object\"\n  },\n  \"metaType\": \"PORTAL_SPECIFIC\",\n  \"name\": \"my_object\",\n  \"primaryDisplayProperty\": \"my_object_property\",\n  \"properties\": [\n    {\n      \"isPrimaryDisplayLabel\": true,\n      \"label\": \"My object property\",\n      \"name\": \"my_object_property\"\n    }\n  ],\n  \"requiredProperties\": [\n    \"my_object_property\"\n  ]\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.hubapi.com/crm-object-schemas/v3/schemas")

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  \"associatedObjects\": [\n    \"CONTACT\"\n  ],\n  \"labels\": {\n    \"plural\": \"My objects\",\n    \"singular\": \"My object\"\n  },\n  \"metaType\": \"PORTAL_SPECIFIC\",\n  \"name\": \"my_object\",\n  \"primaryDisplayProperty\": \"my_object_property\",\n  \"properties\": [\n    {\n      \"isPrimaryDisplayLabel\": true,\n      \"label\": \"My object property\",\n      \"name\": \"my_object_property\"\n    }\n  ],\n  \"requiredProperties\": [\n    \"my_object_property\"\n  ]\n}"

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

{
  "associations": [
    {
      "fromObjectTypeId": "2-123456",
      "id": "123",
      "name": "my_object_to_contact",
      "toObjectTypeId": "0-1"
    }
  ],
  "createdAt": "2020-02-20T18:07:11.390Z",
  "fullyQualifiedName": "p7878787_my_object\"",
  "id": "123456",
  "labels": {
    "plural": "My objects",
    "singular": "My object"
  },
  "metaType": "PORTAL_SPECIFIC",
  "name": "my_object",
  "primaryDisplayProperty": "my_object_property",
  "properties": [
    {
      "archived": false,
      "calculated": false,
      "createdAt": "2020-02-20T18:07:11.802Z",
      "displayOrder": -1,
      "externalOptions": false,
      "fieldType": "text",
      "groupName": "my_object_information",
      "hasUniqueValue": false,
      "label": "My object property",
      "name": "my_object_property",
      "type": "string",
      "updatedAt": "2020-02-20T18:07:11.802Z"
    }
  ],
  "requiredProperties": [
    "my_object_property"
  ],
  "searchableProperties": [
    "my_object_property"
  ],
  "updatedAt": "2020-02-20T18:09:07.555Z"
}

{
  "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"
  }
}