diff --git a/OpenAI/Packages/com.openai.unity/Runtime/Realtime/ConversationItemTruncateRequest.cs b/OpenAI/Packages/com.openai.unity/Runtime/Realtime/ConversationItemTruncateRequest.cs
index 98ecc00..3fc4b6a 100644
--- a/OpenAI/Packages/com.openai.unity/Runtime/Realtime/ConversationItemTruncateRequest.cs
+++ b/OpenAI/Packages/com.openai.unity/Runtime/Realtime/ConversationItemTruncateRequest.cs
@@ -47,7 +47,7 @@ public ConversationItemTruncateRequest(string itemId, int contentIndex, int audi
         /// The index of the content part to truncate. Set this to 0.
         /// </summary>
         [Preserve]
-        [JsonProperty("content_index")]
+        [JsonProperty("content_index", DefaultValueHandling = DefaultValueHandling.Include)]
         public int ContentIndex { get; }
 
         /// <summary>