Reply only to top-level comments on folders
Same one-level threading rule as file comments, on public folder comment APIs. Product text names the folder context.
Why this happens
createPublicFolderPageComment rejects replies whose parent is already a reply. Keeps folder discussion flat beyond one nested layer.
Diagnose and fix
1. Reply to a top-level folder comment only.
2. Enable Public folder comments if posting is disabled entirely.
3. No admin knob for deeper threads.
4. File pages use the file-specific sibling article.