post https://api.projectmanager.com/api/data/workspaces//join
Invite a specific user to join a Workspace to which the current user has administrator rights.
A single User may have access to multiple Workspaces, although they can only be logged on to one Workspace at a time. This API lists all Workspaces to which the currently logged on user is entitled to access. To determine which Workspace a user is currently logged on use the /api/data/me endpoint.
This API allows you to invite a specific an invitation to join a specific Workspace.