curl --request POST \
  --url https://api.hubapi.com/marketing/v4/email/single-send \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "emailId": 123,
  "message": {
    "to": "<string>",
    "bcc": [
      "<string>"
    ],
    "cc": [
      "<string>"
    ],
    "from": "<string>",
    "replyTo": [
      "<string>"
    ],
    "sendId": "<string>"
  },
  "contactProperties": {},
  "customProperties": {}
}
'

import requests

url = "https://api.hubapi.com/marketing/v4/email/single-send"

payload = {
    "emailId": 123,
    "message": {
        "to": "<string>",
        "bcc": ["<string>"],
        "cc": ["<string>"],
        "from": "<string>",
        "replyTo": ["<string>"],
        "sendId": "<string>"
    },
    "contactProperties": {},
    "customProperties": {}
}
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({
    emailId: 123,
    message: {
      to: '<string>',
      bcc: ['<string>'],
      cc: ['<string>'],
      from: '<string>',
      replyTo: ['<string>'],
      sendId: '<string>'
    },
    contactProperties: {},
    customProperties: {}
  })
};

fetch('https://api.hubapi.com/marketing/v4/email/single-send', 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/marketing/v4/email/single-send",
  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([
    'emailId' => 123,
    'message' => [
        'to' => '<string>',
        'bcc' => [
                '<string>'
        ],
        'cc' => [
                '<string>'
        ],
        'from' => '<string>',
        'replyTo' => [
                '<string>'
        ],
        'sendId' => '<string>'
    ],
    'contactProperties' => [
        
    ],
    'customProperties' => [
        
    ]
  ]),
  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/marketing/v4/email/single-send"

	payload := strings.NewReader("{\n  \"emailId\": 123,\n  \"message\": {\n    \"to\": \"<string>\",\n    \"bcc\": [\n      \"<string>\"\n    ],\n    \"cc\": [\n      \"<string>\"\n    ],\n    \"from\": \"<string>\",\n    \"replyTo\": [\n      \"<string>\"\n    ],\n    \"sendId\": \"<string>\"\n  },\n  \"contactProperties\": {},\n  \"customProperties\": {}\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/marketing/v4/email/single-send")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"emailId\": 123,\n  \"message\": {\n    \"to\": \"<string>\",\n    \"bcc\": [\n      \"<string>\"\n    ],\n    \"cc\": [\n      \"<string>\"\n    ],\n    \"from\": \"<string>\",\n    \"replyTo\": [\n      \"<string>\"\n    ],\n    \"sendId\": \"<string>\"\n  },\n  \"contactProperties\": {},\n  \"customProperties\": {}\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.hubapi.com/marketing/v4/email/single-send")

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  \"emailId\": 123,\n  \"message\": {\n    \"to\": \"<string>\",\n    \"bcc\": [\n      \"<string>\"\n    ],\n    \"cc\": [\n      \"<string>\"\n    ],\n    \"from\": \"<string>\",\n    \"replyTo\": [\n      \"<string>\"\n    ],\n    \"sendId\": \"<string>\"\n  },\n  \"contactProperties\": {},\n  \"customProperties\": {}\n}"

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

{
  "statusId": "<string>",
  "completedAt": "2023-11-07T05:31:56Z",
  "eventId": {
    "created": "2023-11-07T05:31:56Z",
    "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a"
  },
  "message": "<string>",
  "requestedAt": "2023-11-07T05:31:56Z",
  "startedAt": "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"
  }
}