A NMI (National Meter Identifier) is an identifier for on-market connection points. As you are part of an Embedded Network, you don’t require a NMI.
There will be one NMI for the entire site, as this is the supply point the retailer sells energy to in bulk.
You will have your own meter number, this is a serial number detailed on your individual meter. These meter numbers are meters are replaced. You can find your meter number detailed on your invoice.