REST call for find-unmapped-volumes

Hi All,

I'm trying to query a VPLEX cluster for unmapped volumes using a REST Post in Powershell, but getting a 523 syntax error. Would anyone know what's not right about this below? 

Invoke-RestMethod -Uri https:// /vplex/export+storage-view+find-unmapped-volumes  -Headers @{'Username' = 'user'; 'Password' = 'password'} -Method Post

Vplex version 5.5.2

Thanks

Jonathan