diff --git a/kie_api/kling3_video.py b/kie_api/kling3_video.py
index 5cda05f..5f898ef 100644
--- a/kie_api/kling3_video.py
+++ b/kie_api/kling3_video.py
@@ -236,6 +236,8 @@ def _build_kling3_payload(
         payload_input["prompt"] = prompt
         payload_input["sound"] = bool(sound)
     else:
+        # KIE expects the sound field to be present; multi-shot requires it to be false.
+        payload_input["sound"] = False
         multi_prompt = _parse_multi_prompt_text(shots_text)
         total_duration = sum(int(item["duration"]) for item in multi_prompt)
         if total_duration < 3 or total_duration > 15:
@@ -401,6 +403,13 @@ def run_kling3_video_from_request(
     payload_input = payload.get("input")
     if not isinstance(payload_input, dict):
         raise _validation_error("request payload must include an input object.")
+    # Backward compatibility for older preflight payloads saved before `sound`
+    # was always included.
+    if "sound" not in payload_input:
+        payload = dict(payload)
+        payload_input = dict(payload_input)
+        payload_input["sound"] = False if bool(payload_input.get("multi_shots")) else True
+        payload["input"] = payload_input
 
     _log(log, "Creating Kling 3.0 video task...")
     start_time = time.time()
diff --git a/web/docs/KIE_Kling3_Video.md b/web/docs/KIE_Kling3_Video.md
index 8aa95e1..170b788 100644
--- a/web/docs/KIE_Kling3_Video.md
+++ b/web/docs/KIE_Kling3_Video.md
@@ -26,6 +26,7 @@ Generate Kling 3.0 videos in single-shot or multi-shot mode.
 - `multi_shots=true`:
   - `last_frame` is invalid
   - `sound` is invalid
+  - payload sends `sound: false`
   - shot durations are summed automatically and sent as the final payload duration
 - `aspect_ratio` is always sent in payload.
 - `@element_name` references in prompt(s) must match provided elements.