Amazon API signature - php

Question

I've been attempting to create a signature to amazons API service, however I keep getting
SignatureDoesNotMatch on all my attempts and I honestly can't see what I've done wrong. This is my code;
<?php
require_once('.config.inc.php');
$sercretAccessKey = "XXXXX";
$site = $_GET['site'];
$serviceUrl = "";
$signatureUrl = "";
//UK marketplace
$marketplaceIdNumber = "A1F83G8C2ARO7P";
date_default_timezone_set('America/Phoenix');
$serviceUrl = "https://mws.amazonservices.de/Orders/2013-09-01";
$signatureUrl = "mws.amazonservices.de";
// Get total from 31 days ago
$t1 = date("c", time()-31*24*60*60);
$AccessKey = "AWSAccessKeyId=" . urlencode("xxxxx");
$action = "&Action=" . urlencode("ListOrders");
$fulfillmentChannel = "&FulfillmentChannel.Channel.1=" . urlencode("MFN");
$updateAfter = "&LastUpdatedAfter=" . urlencode($t1);
$marketplaceId = "&MarketplaceId.Id.1=" . urlencode($marketplaceIdNumber);
$orderStatus1 = "&OrderStatus.Status.1=" . urlencode("Unshipped");
$orderStatus2 = "&OrderStatus.Status.2=" . urlencode("PartiallyShipped");
$sellerID = "&SellerId=" . urlencode("xxxx");
$signatureMethod = "&SignatureMethod=" . urlencode("HmacSHA256");
$signatureVersion = "&SignatureVersion=" . urlencode("2");
$timeStamp = "&Timestamp=" . urlencode(date("c"));
$version = "&Version=" . urlencode("2013-09-01");
$stringToSignature =
"POST\n" .
"$signatureUrl\n" .
"/Orders/2013-09-01\n" .
$AccessKey . $action . $fulfillmentChannel . $updateAfter . $marketplaceId . $orderStatus1 . $orderStatus2 . $sellerID . $signatureMethod . $signatureVersion . $timeStamp . $version;
$signatureCode = hash_hmac('sha256', $stringToSignature, $sercretAccessKey, true);
$signatureCodeBaseEncoded = base64_encode($signatureCode);
$signatureCodeEncoded = urlencode($signatureCodeBaseEncoded);
$signature = "&Signature=" . $signatureCodeEncoded;
$targetURL = $serviceUrl . "?" . $AccessKey . $action . $fulfillmentChannel . $updateAfter . $marketplaceId . $orderStatus1 . $orderStatus2 . $sellerID . $signatureMethod . $signatureVersion . $timeStamp . $version . $signature;
// create context
$context = array('header' => 'Content-Type: text/xml');
$ci = curl_init($targetURL);
curl_setopt($ci, CURLOPT_POST, 1);
curl_setopt($ci, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ci, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ci, CURLOPT_POSTFIELDS,"xmlRequest");
$result = curl_exec($ci);
echo $result;
?>
In theory this should work. I've followed their tutorials and followed what their scratchpad told me. So my request should be in canonical format.
Any help would be great!
I should probably note that the only way I can get any response from amazon is through the german serviceurl.