This section is currently reworked to incorporate changes of version 4.0
com.easesolutions.jira.plugins.requirements/1.0/tree/<projectkey>/foldertree/<folderid>
Folder ID for root folders is -1.
Example
GET https://jira.example.com/rest/com.easesolutions.jira.plugins.requirements/1.0/tree/ABC/foldertree/123