$client = new Client([
'base_uri' => 'http://localhost',
]);
$response = $client->request('POST', '/API/customerOrder/createOrder.php', [
'json' =>[
'SKU_QUANTITY' => [9,7,8],// we send the array of 3 elements to specific ID array.
'CUSTOMER_ID'=>[12,23,34] // This is the array which contain ID.
]
]);