Consolidate is done at the VM level, not the vApp level. At least that's true in the GUI level.
In pure REST, consolidate is a POST command like
POST /api/vApp/vm-78c3771e-465e-496d-9bfe-c6ea6a1de79e/action/consolidate
Even in this example, I think it's only going to consolidate the single VM inside the vApp (not all VMs inside the vApp).
Maybe you're looking in the wrong place?