diff --git a/src/Api/Filter.php b/src/Api/Filter.php
index 9f81404..a9b980d 100644
--- a/src/Api/Filter.php
+++ b/src/Api/Filter.php
@@ -37,7 +37,7 @@ public function toArray()
             ];
         }
 
-        if ($this->operator === 'IN') {
+        if ($this->operator === 'IN' || $this->operator === 'NOT_IN') {
             return [
                 'propertyName' => $this->property,
                 'operator'     => $this->operator,
@@ -76,4 +76,4 @@ protected function translateOperator($operator): string
             'not like'   => 'NOT_CONTAINS_TOKEN'
         ], strtolower($operator), $operator);
     }
-}
\ No newline at end of file
+}