public function refund(Varien_Object $payment, $amount)
 {
     $transaction_number = $payment->getLastTransId();
     $return_number = $payment->getOrder()->getIncrementId();
     // Convert amount to cents
     $amount = $this->getHelper()->convertToCents($amount);
     $apiReturn = new Tritac_CapayableApiClient_Models_InvoiceCreditRequest($transaction_number, $return_number, $amount);
     // Fetch Store ID and key pair for selected store (admin store is always 0)
     // Create new admin client, with correct key pair to process refund
     $store_id = $payment->getOrder()->getStore()->getId();
     $public_key = Mage::getStoreConfig('capayable/capayable/public_key', $store_id);
     $secret_key = Mage::getStoreConfig('capayable/capayable/secret_key', $store_id);
     $adminClient = new Tritac_CapayableApiClient_Client($public_key, $secret_key, $this->_helper->getMode());
     $isAccepted = $adminClient->creditInvoice($apiReturn);
     return $this;
 }