vfs.fs.size # FSNAME, pfree is not supported

Good morning, if I use the zabbix discovery feature, it will display information related to vfs.fs.size # FSNAME, free, showing the information correctly, now if I use vfs.fs.size FSNAME, pfree it shows as unsupported, if I inform what would be the vfs.fs.size [/, pfree] partition it shows me the result, ie it is something related to the discovery, because if I excute the command pointing the non-partitions error, it informs correctly.