Node Opcua / QtOpcUa - Method Calls

Question

I have a Node OPC Server which I connect to with a Qt application using the QtOpcUa client library.

On my server I define a method that's basically a crude historic access request as HDA support is not yet available, it takes in a start_date and end_date then queries a database for the relevant values which it returns in an array.

It looks a bit like this:

const deviceTrends = namespace.addObject({
    organizedBy: deviceObject,
    browseName: strings.TREND_NODE
})

const method = namespace.addMethod(deviceTrends,{

nodeId: strings.NSI + part.name + "-Trend",
browseName: part.name + "-Trend",

inputArguments:  [
    {
        name:"start_date",
        description: { text: "Trend Start Date" },
        dataType: opcua.DataType.DateTime        
    },{
        name:"end_date",
        description: { text: "Trend End Date" },
        dataType: opcua.DataType.DateTime
    }
    ],

outputArguments: [{
        name:"Trend",
        description:{ text: "Trend Data from start_date to end_date" },
        dataType: opcua.DataType.String ,
        valueRank: 1
}]});

method.bindMethod(function(inputArguments,context,callback) {

console.log("called")

const start = inputArguments[0].value;
const end =  inputArguments[1].value;

console.log("Start: ", start);
console.log("End: ", end);

let sql = `SELECT Date date,
                    Name name,
                    Value value
                FROM Trends
                WHERE DateTime >= ? AND DateTime <= ?`;

var result = []

db.each(sql, [start, end], (err, row) =>
{
    result.push(`${row.date}: ${row.name} - ${row.value}`)
})

console.log(result)

const callMethodResult = {
    statusCode: opcua.StatusCodes.Good,
    outputArguments: [{
            dataType: opcua.DataType.String,
            arrayType: opcua.VariantArrayType.Array,
            value :result
    }]
};
callback(null,callMethodResult);});}

I can see this in a client such as Prosys and call the method which works okay:

However I can't seem to call this method from Qt, I've cut out the packaging of arguments and the result handler (it just lists out the received params):

QOpcUaNode* n = devices[deviceName].client->node("ns=1;s=Speed-Trend");

connect(n, &QOpcUaNode::methodCallFinished, [this, deviceName](QString methodNodeId, QVariant result, QOpcUa::UaStatusCode status)
{
    qDebug() << " Response received ";
    this->handleNodeTrendResponse(deviceName, methodNodeId, result, status);

});

n->callMethod(n->nodeId(), args);

Trace:

Requesting Trend: From  QDateTime(2018-10-07 13:13:56.766 BST Qt::TimeSpec(LocalTime))  TO  QDateTime(2018-10-07 13:14:05.390 BST Qt::TimeSpec(LocalTime))

qt.opcua.plugins.open62541: Could not call method: BadNodeIdInvalid

Response received [Output from method result handler]
Device Name:  "speed-device"
Method Node Id:  "ns=1;s=Speed-Trend"
Result:  QVariant(Invalid)
Result to List: <<  ()
Status:  QOpcUa::UaStatusCode(BadNodeIdInvalid)

I also can't seem to find the method on other clients too, this is from an OPC UA Client application on my phone which shows nothing under the Trends object:

Everything else seems accessible, I can request variables, setup monitoring all fine.

Is there something I'm just missing here or is it an issue with QtOpcUa and other clients?

I can work around this by creating variables instead to capture input and output arguments and a boolean to represent a method call but it's a lot neater to tie everything up in a single method.

Thanks