Follow the On-board fleet devices guide to add a device to the 'world' site. The following device resource should be created.
PUT https://api.mk.io/api/v1/projects/project_name/fleet/devices/device1
{
"metadata": {
"displayName": "Device 1"
},
"spec": {
"siteName": "world",
"locationId": "a7dafdba-4923-4317-aad1-dc76284b85b5"
}
}