Neteller TransferOut with PHP / CURL - php

Question

I'm having some problems using the Neteller API to transfer money out of our merchant account to a user. I've succcessfully received the accessToken, however when I try using transferOut I just get invalid credentials? The code I'm using is:
$headers = array(
"Content-type" => "application/json",
"Authorization" => "Bearer " . $accessToken
);
//build the request body structure
$requestParams = array(
"payeeProfile" => array(
"email" => $the_email_address_to_send_to
),
"transaction" => array(
"merchantRefId" => $transaction_id,
"amount" => $amount,
"currency" => $currencyCode
)
);
// encode the requestParams to a string
$requestParams = json_encode($requestParams);
// The curl stuff
$curl = curl_init();
curl_setopt($curl, CURLOPT_POST, 1);
curl_setopt($curl, CURLOPT_URL, "https://api.neteller.com/v1/transferOut");
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
curl_setopt($curl, CURLOPT_POSTFIELDS, $requestParams);
curl_setopt($curl, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
// Ok lets send this lovely looking curl over
$serverOutput = json_decode(curl_exec($curl));
Obviously all variables ($transaction_id, $amount, $currency) are set appropriately. However the response I get back is:
stdClass Object
(
[error] => stdClass Object
(
[code] => 5279
[message] => Authentication credentials are invalid
)
)
I'm confused, surely the accessToken is the credentials I need, and theyve already been received. Am I meant to include anything else in the transferOut curl postfields?
Thanks in advance

Answer 1

As per user3584460's comment:
$headers does not look OK - try $headers = array("Content-type: application/json", "Authorization: Bearer " . $accessToken);. At least this is the format according to http://php.net/manual/en/function.curl-setopt.php
Note, the Merchant Ref ID also needs to be a certain length. unsure what - can't find reference, but 8 characters is not long enough.