diff --git a/plugins/federator/contentnation.php b/plugins/federator/contentnation.php
index a77f846..daf2b50 100644
--- a/plugins/federator/contentnation.php
+++ b/plugins/federator/contentnation.php
@@ -735,7 +735,7 @@ class ContentNation implements Connector
             'Content-Type: application/json',
             'Signature: ' . $signatureHeader,
             'Accept: application/json',
-            'Username: ' . $sender->id,
+            'Username: ' . 'ap:' . $sender->id,
         ];
 
         curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);