Cannot reach the hub API - check that the hub is running.
No devices have checked in yet.
On an IoT device, run a client that pings the hub (every 30 s by default):
curl -s -X POST http://HUB_IP:30303/ping \
-H 'Content-Type: application/json' \
-d '{"name": "my-device"}'
# or use the provided client:
./hub_client.sh HUB_IP my-device