<?php
require __DIR__ . '/vendor/autoload.php';

use Zend\Http\Client;
use Zend\Json\Json;

$apiKey = 'YOUR API KEY';
$apiUrl = 'https://api.taxjar.com/v2/taxes';

$client = new Client($apiUrl);
$client->setMethod('POST');
$client->setHeaders([
  'Authorization' => 'Bearer ' . $apiKey,
  'Content-Type' => 'application/json'
]);

$data = [
  'to_country' => 'US',
  'to_zip' => '92101',
  'to_state' => 'CA',
  'to_city' => '',
  'to_street' =>  '',
  'amount' => 99.99,
  'shipping' => 5,
  'line_items' => [
      [
          'id' => 135,
          'quantity' => 1,
          'unit_price' => 99.99,
          'discount' => 0,
          'product_tax_code' => '20010' 
      ]
  ]
];

$client->setRawBody(Json::encode($data));

try {
  $response = $client->send();
  echo $response->getBody();
} catch (Exception $e) {
  // Log exception
}