To get the folders based on the containerId, you will need to run the API found at the URL below to get the top folders and use the same to get sub folders.

Top Folder API - https://aps.autodesk.com/en/docs/data/v2/reference/http/hubs-hub_id-projects-project_id-topFolders-GET/

Sub Folders API - https://aps.autodesk.com/en/docs/data/v2/reference/http/projects-project_id-folders-folder_id-GET/

Note that containerId is same as the project id without the b.