diff --git a/src/Request/SubscribersPostRequest.php b/src/Request/SubscribersPostRequest.php
index d45607c..189455f 100644
--- a/src/Request/SubscribersPostRequest.php
+++ b/src/Request/SubscribersPostRequest.php
@@ -157,11 +157,11 @@ private function writeSubscriberDataToXml(\XMLWriter $xmlWriter, SubscriberInfo
             $xmlWriter->writeElement('Phone', $subscriberInfo->getPhone());
         }
 
-        if (!empty($subscriberInfo->getFirstName())) {
+        if (!empty($subscriberInfo->getFirstname())) {
             $xmlWriter->writeElement('FirstName', $subscriberInfo->getFirstName());
         }
 
-        if (!empty($subscriberInfo->getLastName())) {
+        if (!empty($subscriberInfo->getLastname())) {
             $xmlWriter->writeElement('LastName', $subscriberInfo->getLastName());
         }