How to send money to paypal using php

I was looking for the same issue, here’s what is working for me.
Tested in ‘sandbox’ mode and using NVP (instead of SOAP).
Your server must support CURL, in order to verify it use:

<?php
echo 'curl extension/module loaded/installed: ';
echo ( !extension_loaded('curl')) ? 'no' : 'yes';
echo "<br />\n";
phpinfo(INFO_MODULES); // just to be sure
?>

If is not loaded or installed ask to your hostmaster or get it here, otherwise go ahead:

<?php
// code modified from source: https://cms.paypal.com/cms_content/US/en_US/files/developer/nvp_MassPay_php.txt
// documentation: https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/howto_api_masspay
// sample code: https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/library_code

// eMail subject to receivers
$vEmailSubject="PayPal payment";

/** MassPay NVP example.
 *
 *  Pay one or more recipients. 
*/

// For testing environment: use 'sandbox' option. Otherwise, use 'live'.
// Go to www.x.com (PayPal Integration center) for more information.
$environment="sandbox"; // or 'beta-sandbox' or 'live'.

/**
 * Send HTTP POST Request
 *
 * @param string The API method name
 * @param string The POST Message fields in &name=value pair format
 * @return array Parsed HTTP Response body
 */
function PPHttpPost($methodName_, $nvpStr_)
{
 global $environment;

 // 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('my_api_username');
 $API_Password = urlencode('my_api_password');
 $API_Signature = urlencode('my_api_signature');
 $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('51.0');

 // 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;
}

// Set request-specific fields.
$emailSubject = urlencode($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' => "[email protected]", 
    'amount' => "20.00",
    'uniqueID' => "id_001", // 13 chars max
    'note' => " payment of commissions"), // I recommend use of space at beginning of string.
  1 => array(
    'receiverEmail' => "[email protected]",
    'amount' => "162.38",
    'uniqueID' => "A47-92w", // 13 chars max, available in 'My Account/Overview/Transaction details' when the transaction is made 
    'note' => " payoff of what I owed you"  // space again at beginning.
  )
);
$receiversLenght = count($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 = PPHttpPost('MassPay', $nvpStr);

if("SUCCESS" == strtoupper($httpParsedResponseAr["ACK"]) || "SUCCESSWITHWARNING" == strtoupper($httpParsedResponseAr["ACK"]))
{
 exit('MassPay Completed Successfully: ' . print_r($httpParsedResponseAr, true));
}
else
{
 exit('MassPay failed: ' . print_r($httpParsedResponseAr, true));
}

?>

Good luck!