Fiware Scorpio appending new attribute to existing entity

I tried to append a new entity to an existing entity. Same as in the official example on: https://scorpio.readthedocs.io/en/latest/API_walkthrough.html#updating-an-entity-appending-to-an-entity

Try to append attribute humidity:

curl localhost:9090/ngsi-ld/v1/entities/house2%3Asmartrooms%3Aroom1/attrs -s -S -X PATCH -H 'Content-Type: application/json' -H 'Link: https://pastebin.com/raw/Mgxv2ykn' -d @- <<EOF
{
        "humidity": {
        "value": 34,
        "unitCode": "PER",
        "type": "Property",
        "providedBy": {
                "type": "Relationship",
                "object": "smartbuilding:house2:sensor2222"
        }
  }
}

But I receive the error:

{
  https://uri.etsi.org/ngsi-ld/default-context/notUpdated : [ {
    https://uri.etsi.org/ngsi-ld/attributeName : {
      "@id" : https://uri.etsi.org/ngsi-ld/default-context/humidity
    },
    https://uri.etsi.org/ngsi-ld/reason : "attribute not found in original entity"
  } ]
}

Can anybody tell me, if they encounter the same problem? Or how to fix this?

Thank you in advance!