Paypal PHP MassPay API got declined all the time - php

Question

We are using Paypal MassPay API to pay for our clients online. Every time we try to send out Mass payment via the API (look at the code below), although it does NOT throw any error, and the money got sent out successfully (logs on Paypal), but then in less than 20 seconds we always receive another message on paypal saying that fund was declined/rejected right away (70% of the time).
So first like this:
Then for majority of the time it becomes to this:
It works perfectly fine when we upload our csv to paypal and do mass payment directly.
Any ideas?
=======
protected function PPHttpPost($methodName_, $nvpStr_){
$environment = 'live'; // or 'beta-sandbox' or 'live'.
// Set up your API credentials, PayPal end point, and API version.
// How to obtain API credentials:
// https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/e_howto_api_NVPAPIBasics#id084E30I30RO
$API_UserName = urlencode('xxxx');
$API_Password = urlencode('xxxx');
$API_Signature = urlencode('xxxxxxxx');
$API_Endpoint = "https://api-3t.paypal.com/nvp";
if("sandbox" === $environment || "beta-sandbox" === $environment)
{
$API_Endpoint = "https://api-3t.$environment.paypal.com/nvp";
}
$version = urlencode('93');
// Set the curl parameters.
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $API_Endpoint);
curl_setopt($ch, CURLOPT_VERBOSE, 1);
// Turn off the server and peer verification (TrustManager Concept).
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POST, 1);
// Set the API operation, version, and API signature in the request.
$nvpreq = "METHOD=$methodName_&VERSION=$version&PWD=$API_Password&USER=$API_UserName&SIGNATURE=$API_Signature$nvpStr_";
// Set the request as a POST FIELD for curl.
curl_setopt($ch, CURLOPT_POSTFIELDS, $nvpreq);
// Get response from the server.
$httpResponse = curl_exec($ch);
if(!$httpResponse)
{
exit("$methodName_ failed: " . curl_error($ch) . '(' . curl_errno($ch) .')');
}
// Extract the response details.
$httpResponseAr = explode("&", $httpResponse);
$httpParsedResponseAr = array();
foreach ($httpResponseAr as $i => $value)
{
$tmpAr = explode("=", $value);
if(sizeof($tmpAr) > 1)
{
$httpParsedResponseAr[$tmpAr[0]] = $tmpAr[1];
}
}
if((0 == sizeof($httpParsedResponseAr)) || !array_key_exists('ACK', $httpParsedResponseAr))
{
exit("Invalid HTTP Response for POST request($nvpreq) to $API_Endpoint.");
}
return $httpParsedResponseAr;
}
public function actionSend(){
$vEmailSubject = 'XXXX payment - Paypal';
$emailSubject = urlencode($vEmailSubject);
$receiverType = urlencode('EmailAddress');
$currency = urlencode('USD'); // or other currency ('GBP', 'EUR', 'JPY', 'CAD', 'AUD')
// Receivers
// Use '0' for a single receiver. In order to add new ones: (0, 1, 2, 3...)
// Here you can modify to obtain array data from database.
$receivers = array(
0 => array(
'receiverEmail' => $model->paypal,
'amount' => $model->money,
'uniqueID' => time(), // 13 chars max
'note' => "XXXX payment",
),
);
$receiversLenght = count($receivers);
// Add request-specific fields to the request string.
$nvpStr="&&EMAILSUBJECT=$emailSubject&RECEIVERTYPE=$receiverType&CURRENCYCODE=$currency";
$receiversArray = array();
for($i = 0; $i < $receiversLenght; $i++)
{
$receiversArray[$i] = $receivers[$i];
}
foreach($receiversArray as $i => $receiverData)
{
$receiverEmail = urlencode($receiverData['receiverEmail']);
$amount = urlencode($receiverData['amount']);
$uniqueID = urlencode($receiverData['uniqueID']);
$note = urlencode($receiverData['note']);
$nvpStr .= "&L_EMAIL$i=$receiverEmail&L_Amt$i=$amount&L_UNIQUEID$i=$uniqueID&L_NOTE$i=$note";
}
// Execute the API operation; see the PPHttpPost function above.
$httpParsedResponseAr = $this->PPHttpPost('MassPay', $nvpStr);
if("SUCCESS" == strtoupper($httpParsedResponseAr["ACK"]) || "SUCCESSWITHWARNING" == strtoupper($httpParsedResponseAr["ACK"]))
{
echo "success";
}else{
echo "something is wrong";
}
}
......