Vault: Get Expiring Cards: Error Message: 987 Invalid transaction: max attempts reached

I am implementing Vault and have stored some credit cards in Vault. 

I am attempting to get dataKeys for the expiring cards using 'res_get_expiring'. However, it is failing with response code 987 with the following message:

[Message] => Invalid transaction: max attempts reached

Is there any limit on the number of times res_get_expiring can be tried in a day? 

Can it be due to my code? Here is my code (PHP)

public function getExpiringCards() 
 {
    $dataKeys = false;
    $txnArray=array('type'=>'res_get_expiring',
    );
    $mpgTxn = new mpgTransaction($txnArray);
 
   $mpgRequest = new mpgRequest($mpgTxn);
   if ($mpgRequest)
   {
     $mpgRequest->setProcCountryCode($this->countryCode); 
     $mpgHttpPost =new mpgHttpsPost($this->store_id,$this->api_token,$mpgRequest);
 
     if ($mpgHttpPost)
     {
        $res=$mpgHttpPost->getMpgResponse();
        if ($res)
        {
          $this->response = $res; 
          if ($res->getResponseCode() < 50 ) // OK 
          { 
             $dataKeys = $res->getDataKeys();
          } 
        }
     }
   }
  return $dataKeys;
 }