diff --git a/src/mcp_synology_filestation/client.py b/src/mcp_synology_filestation/client.py
index 10ea729..54de69a 100644
--- a/src/mcp_synology_filestation/client.py
+++ b/src/mcp_synology_filestation/client.py
@@ -262,6 +262,11 @@ class FileStationClient:
         info = self._api_cache[api]
         resolved_version = version if version is not None else info["maxVersion"]
         url = f"{self._base_url}/webapi/{info['path']}"
+        sys.stderr.write(
+            f"[dsm] REQUEST {api}/{method} v{resolved_version} "
+            f"(NAS max={info['maxVersion']})\n"
+        )
+        sys.stderr.flush()
 
         req_params: dict[str, Any] = {
             "api": api,
@@ -295,6 +300,8 @@ class FileStationClient:
 
         code = body.get("error", {}).get("code", 0)
         logger.debug("DSM response: %s/%s — error code %d", api, method, code)
+        sys.stderr.write(f"[dsm] RAW ERROR {api}/{method}: {body!r}\n")
+        sys.stderr.flush()
 
         # Transparent re-auth on session errors (one retry only)
         if code in _SESSION_ERROR_CODES and not _is_retry and self._auth_manager:
diff --git a/src/mcp_synology_filestation/tools/filestation.py b/src/mcp_synology_filestation/tools/filestation.py
index 7fe64b8..2cbafb6 100644
--- a/src/mcp_synology_filestation/tools/filestation.py
+++ b/src/mcp_synology_filestation/tools/filestation.py
@@ -151,7 +151,7 @@ def register_filestation(
                     "limit": limit,
                     "sort_by": sort_by,
                     "sort_direction": sort_direction,
-                    "additional": json.dumps(["size", "time"]),
+                    # DEBUG: no additional — testing if any additional causes 408
                 },
             )
         except SynologyError as e: