Edited point-topic-mcp/src/point_topic_mcp/tools/chart_tools.py:

```diff
@@ -41,7 +41,7 @@
     parsed = urllib.parse.urlparse(url)
     query = urllib.parse.parse_qs(parsed.query)
     query.pop('format', None)
-    query['format'] = 'csv'
+    query['format'] = ['csv']
     csv_url = urllib.parse.urlunparse(parsed._replace(query=urllib.parse.urlencode(query, doseq=True)))
 
     resp = requests.get(csv_url)

```