Redmine

This is an example of a subproject fetched by http://REDMINE_URL/projects.json. As you can see it contains its parent projects id and name. But you are right, the documentation doesn't show it.

{
  "id":26,"name":"Events",
  "identifier":"events",
  "description":"Planning of all events",
  "parent:
    {
    "id":25,
    "name":"Marketing" 
    },
  "status":1,
  "is_public":false,
  "created_on":"2018-06-09T22:27:33Z",
  "updated_on":"2018-06-10T07:00:28Z" 
}