Yes I understand. We just visualise a SmartApp differently. To me it is the app in your cloud that is communicating with SmartThings and managing your cloud connected devices.
In SmartThings device attributes, your sensor data, are updated using device events and for your cloud connected device those events are created using the API POST you referred to.
So for a simple device like a contact sensor you would do a POST
to https://api.smartthings.com/devices/{{deviceId}}/events
with the JSON body:
{
"deviceEvents": [
{
"component": "main",
"capability": "contactSensor",
"attribute": "contact",
"value": "open"
}
]
}
I don’t know why the API reference doesn’t include an example payload in this case.