MQTT Downlink format

when I publish mqtt downlink using mqtt box on topic /in865/gateway/gatewayID/command/down i.e.
{
“devEui”: “DEVICE_EUI”,
“confirmed”: true,
“fPort”: 7,
“data”: “AQID=”
}

then I get error:—>> level=error msg=“integration/mqtt: downlink must have at least one item” downlink_id=0

and when I publish below downlink

{
“devEui”: “DEV_EUI”,
“confirmed”: true,
“fPort”: 7,
“data”: “…”
“object”: {
“temperatureSensor”: {“1”: 25},
“humiditySensor”: {“1”: 32}
}
}

then I get error —>> level=error msg=“integration/mqtt: unmarshal downlink frame error” error=“proto: syntax error (line 6:5): unexpected token “object”” topic=in865/gateway/506f9800000001e9/command/down