--- uc_credit.module
+++ uc_credit.module
@@ -175,6 +175,7 @@
         $txn_types = array(
           UC_CREDIT_AUTH_ONLY => t('Authorization only'),
           UC_CREDIT_AUTH_CAPTURE => t('Authorize and capture immediately'),
+          UC_CREDIT_REFERENCE_SET => t('Set a reference only'),
         );
 
         foreach ($txn_types as $type => $title) {