paypal node.js API malformed request

I'm creating an array for the items field in the JSON doc required to create a paypal payment.

I can create the payment with dummy data, all looks good. However when I use real data via an iteration to create the object, after the .create request I get a MALFORMED_REQUEST error.

Code is:

var items = [];
for(i = 0; i < req.body.parts.length; i++)
{
  part = req.body.parts[i];
  items.push ({"name": part.part_display_name, "description": part.SKU, "sku": part.SKU, "price": part.price, "currency": "USD", "quantity": 1});
};
console.log (items);

Example output:

[ { name: 'Detective Handle Checker Grips',
    description: 'vyctorslab_pistol_2015A_mowrer_handle_detective_checker_black-rubber-and-brass',
    sku: 'vyctorslab_pistol_2015A_mowrer_handle_detective_checker_black-rubber-and-brass',
    price: 50,
    currency: 'USD',
    quantity: 1 },
  { name: 'Detective Hammer',
    description: 'vyctorslab_pistol_2015A_mowrer_hammer_detective_base_steel',
    sku: 'vyctorslab_pistol_2015A_mowrer_hammer_detective_base_steel',
    price: 50,
    currency: 'USD',
    quantity: 1 } ]

It certainly looks like the required JSON, however when creating the payment as follows:

var payment = {
  "intent": "order",
  "payer": {"payment_method": "paypal"},
  "redirect_urls": {"return_url":  return_url, "cancel_url": cancel_url},
  "transactions": [
  {"amount": req.body.total_price, "description": "Maykrlab model purchase.","item_list": items }
  ]
};

Output is:

{ intent: 'order',
  payer: { payment_method: 'paypal' },
  redirect_urls:
   { return_url: 'http://ift.tt/1E0AbEk',
     cancel_url: 'http://ift.tt/186R2bT' },
  transactions:
   [ { amount: 500,
       description: 'Maykrlab model purchase.',
       item_list: [Object] } ] }

All still seems to be OK, the [Object] in the last line above is the items JSON created earlier.

However, the call to paypal is returned with:

{"response":{"name":"MALFORMED_REQUEST","message":"Incoming JSON request does not map to API request","information_link"
:"http://ift.tt/1eUIDbv","debug_id":"4f5997d207eca","httpStatusCode
":400},"httpStatusCode":400}

I believe I'm not correctly turning the items object created by the iteration into the correct format for posting to the paypal API. Can anyone advise? It's probably a case of needing to use .stringify in some place?