curl --request POST \
  --url https://api.smartermeasure.com/v3/users \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "GroupKey": 123,
  "FirstName": "<string>",
  "LastName": "<string>",
  "Email": "<string>",
  "InternalID": "<string>",
  "EthnicityID": 123,
  "AgeRange": "<string>",
  "HowManyCoursesTaken": "<string>",
  "Custom": {}
}
'

import requests

url = "https://api.smartermeasure.com/v3/users"

payload = {
    "GroupKey": 123,
    "FirstName": "<string>",
    "LastName": "<string>",
    "Email": "<string>",
    "InternalID": "<string>",
    "EthnicityID": 123,
    "AgeRange": "<string>",
    "HowManyCoursesTaken": "<string>",
    "Custom": {}
}
headers = {
    "Authorization": "Basic <encoded-value>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: 'Basic <encoded-value>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    GroupKey: 123,
    FirstName: '<string>',
    LastName: '<string>',
    Email: '<string>',
    InternalID: '<string>',
    EthnicityID: 123,
    AgeRange: '<string>',
    HowManyCoursesTaken: '<string>',
    Custom: {}
  })
};

fetch('https://api.smartermeasure.com/v3/users', 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.smartermeasure.com/v3/users",
  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([
    'GroupKey' => 123,
    'FirstName' => '<string>',
    'LastName' => '<string>',
    'Email' => '<string>',
    'InternalID' => '<string>',
    'EthnicityID' => 123,
    'AgeRange' => '<string>',
    'HowManyCoursesTaken' => '<string>',
    'Custom' => [
        
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Basic <encoded-value>",
    "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.smartermeasure.com/v3/users"

	payload := strings.NewReader("{\n  \"GroupKey\": 123,\n  \"FirstName\": \"<string>\",\n  \"LastName\": \"<string>\",\n  \"Email\": \"<string>\",\n  \"InternalID\": \"<string>\",\n  \"EthnicityID\": 123,\n  \"AgeRange\": \"<string>\",\n  \"HowManyCoursesTaken\": \"<string>\",\n  \"Custom\": {}\n}")

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

	req.Header.Add("Authorization", "Basic <encoded-value>")
	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.smartermeasure.com/v3/users")
  .header("Authorization", "Basic <encoded-value>")
  .header("Content-Type", "application/json")
  .body("{\n  \"GroupKey\": 123,\n  \"FirstName\": \"<string>\",\n  \"LastName\": \"<string>\",\n  \"Email\": \"<string>\",\n  \"InternalID\": \"<string>\",\n  \"EthnicityID\": 123,\n  \"AgeRange\": \"<string>\",\n  \"HowManyCoursesTaken\": \"<string>\",\n  \"Custom\": {}\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.smartermeasure.com/v3/users")

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

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Basic <encoded-value>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"GroupKey\": 123,\n  \"FirstName\": \"<string>\",\n  \"LastName\": \"<string>\",\n  \"Email\": \"<string>\",\n  \"InternalID\": \"<string>\",\n  \"EthnicityID\": 123,\n  \"AgeRange\": \"<string>\",\n  \"HowManyCoursesTaken\": \"<string>\",\n  \"Custom\": {}\n}"

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