Help with Shopify API for a private app by Tony Small

Hoping someone can help me. I can't get any of the shopify API libraries to work. Because it's private, I don't have to do the authentification stuff (so should be easier.) My code below works when I change it to retrieve a list of products, but when I try to add a new one, I get a "Required parameter missing" error. Yet the documentation says all I need is a title and a type.

Any ideas? Thanks!

$adb_url="https://<myapikey>:<myapisecret>@<myurl>.myshopify.com/admin&quot;;

$adb_option_defaults = array(
    CURLOPT_HEADER => false,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT => 2
  ); 

// ArangoDB REST function.
// Connection are created demand and closed by PHP on exit.
function adb_rest($method,$uri,$querry=NULL,$json=NULL,$options=NULL){
  global $adb_url,$adb_handle,$adb_option_defaults;

  // Connect 
  if(!isset($adb_handle)) $adb_handle = curl_init();

  // Compose querry
  $options = array(
    CURLOPT_URL => $adb_url.$uri."?".$querry,
    CURLOPT_CUSTOMREQUEST => $method, // GET POST PUT PATCH DELETE HEAD OPTIONS 
    CURLOPT_POSTFIELDS => $json,
  ); 
  curl_setopt_array($adb_handle,($options + $adb_option_defaults)); 

  // send request and wait for responce
  $responce =  json_decode(curl_exec($adb_handle),true);

  echo "Responce from DB: \n";
  print_r($responce);
  return($responce);
}


$responce = adb_rest("POST","/products.json","",'{"product": {"title": "Burton Custom Freestlye 151","product_type": "Food"');
var_dump($responce);