unknown for flat provider network

root@aio1-utility-container-67ef1407:/# neutron net-create public --shared --provider:physical_network public --provider:network_type flat
Invalid input for operation: physical_network 'public' unknown for flat provider network.
Neutron server returns request_ids: ['req-aa83f5d9-a783-48ca-960b-96f5a5563847']