the documentation of chirpstack gives:
// Decode uplink function.
//
// Input is an object with the following fields:
// - bytes = Byte array containing the uplink payload, e.g. [255, 230, 255, 0]
// - fPort = Uplink fPort.
// - variables = Object containing the configured device variables.
//
// Output must be an object with the following fields:
// - data = Object representing the decoded payload.
function decodeUplink(input) {
return {
data: {
temp: 22.5
}
};
}
so it seems recvTime argument is not present to be compatible with API from lorawan.