Hello @Stephan Scholz,
welcome to this moderated Azure community forum.
You constructed a DTDL description of a messages that looks like this:
{
"CO2": x,
"IAC": y
...
}
The TTN message that arrived is much more complex and starts at the "decoded_payload" JSON element.
IoT Central does not know anything about the nested message, it wants to map the complete incoming message.
So you either simplify the message send to the IoT Central to only the "decoded_payload" body or you extend the DTDL model so it eventually implements the "decoded_payload" body.
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