I successfully use the API v2 calls to get Solution Folders based on the old three-level solutions hierarchy e.g.
GET /api/v2/solutions/folders
returns a series of objects under `folders`
GET /api/v2/solutions/folders/{id}
and returns a single object under `folder`
Now, since the introduction of nested folders (enhanced knowledge base hierarchy) folders can have subfolders, and in the payload each folder object now returns a boolean value
has_subfolders
However, the API documentation has not been updated. Fortunately the Freshworks devs have been logical in their changes, so by trial and error I managed to work out that the syntax is, similar to the ‘folders in categories’ API route:
GET /api/v2/solutions/folders?parent_id={id}
Happy coding Freshfans!

