Update custom-metadata.mdx

Author: kathayl

src/content/docs/ai-gateway/configuration/custom-metadata.mdx

@@ -14,6 +14,13 @@ Custom metadata in AI Gateway allows you to tag requests with user IDs or other
 * **Enhanced Logging**: Metadata appears in your logs, allowing for detailed inspection and troubleshooting.
 * **Search and Filter**: Use metadata to efficiently search and filter through logged requests.
 
+:::note
+
+
+AI Gateway allows you to pass up to five custom metadata entries per request. If more than five entries are provided, only the first five will be saved; additional entries will be ignored. Ensure your custom metadata is limited to five entries to avoid unprocessed or lost data.
+
+:::
+
 ## Supported Metadata Types
 
 * String