curl --request PATCH \
  --url https://api.gcore.com/cloud/v1/reserved_fixed_ips/{project_id}/{region_id}/{port_id}/connected_devices \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "port_ids": [
    "351b0dd7-ca09-431c-be53-935db3785067",
    "bc688791-f1b0-44eb-97d4-07697294b1e1"
  ]
}
'

{
  "count": 1,
  "results": [
    {
      "instance_id": "bc688791-f1b0-44eb-97d4-07697294b1e1",
      "instance_name": "Virtual Machine 1",
      "ip_assignments": [
        {
          "ip_address": "192.168.123.20",
          "subnet": {
            "cidr": "192.168.13.0/24",
            "created_at": "2019-06-13T13:58:12+0000",
            "enable_dhcp": true,
            "id": "b39792c3-3160-4356-912e-ba396c95cdcf",
            "name": "subnet_3",
            "network_id": "b30d0de7-bca2-4c83-9c57-9e645bd2cc92",
            "project_id": 1337,
            "region": "Luxembourg 1",
            "region_id": 7,
            "tags": [
              {
                "key": "my-tag",
                "read_only": false,
                "value": "my-tag-value"
              }
            ],
            "updated_at": "2019-06-13T13:58:12+0000",
            "available_ips": 250,
            "creator_task_id": "5cc890da-d031-4a23-ac31-625edfa22812",
            "dns_nameservers": [
              "8.8.8.8",
              "8.8.4.4"
            ],
            "gateway_ip": "192.168.13.1",
            "has_router": false,
            "host_routes": [],
            "task_id": null,
            "total_ips": 253
          },
          "subnet_id": "b39792c3-3160-4356-912e-ba396c95cdcf"
        }
      ],
      "network": {
        "created_at": "2019-06-18T11:56:16+0000",
        "creator_task_id": "fd50fdd1-0482-4c9b-b847-fc9924665af6",
        "default": true,
        "external": true,
        "id": "eed97610-708d-43a5-a9a5-caebd2b7b4ee",
        "mtu": 1500,
        "name": "public",
        "port_security_enabled": true,
        "project_id": 1337,
        "region": "Luxembourg 1",
        "region_id": 7,
        "segmentation_id": 9,
        "shared": false,
        "subnets": [
          "f00624ab-41bc-4d54-a723-1673ce32d997",
          "41e0f698-4d39-483b-b77a-18eb070e4c09"
        ],
        "tags": [
          {
            "key": "my-tag",
            "read_only": false,
            "value": "my-tag-value"
          }
        ],
        "task_id": null,
        "type": "vlan",
        "updated_at": "2019-06-18T11:57:00+0000"
      },
      "port_id": "351b0dd7-ca09-431c-be53-935db3785067"
    }
  ]
}