client.WriteValue(endpointDescriptor, nodeDescriptor, attributeData);

client.WriteValue(endpointDescriptor, nodeDescriptor, uaGenericObject);

static void Main(string[] args){
            UAEndpointDescriptor endpointDescriptor = "opc.tcp://localhost:48030/";
            UANodeDescriptor     nodeDescriptor     = "ns=2;i=6009";
 
            using(var client = new EasyUAClient()){
                try{
                    var attributeData = client.Read(endpointDescriptor, nodeDescriptor);
                    if(attributeData?.Value is UAGenericObject uaGenericObject){
                        var fieldData = (((StructuredData)uaGenericObject.GenericData)?.FieldData);
                        if(fieldData == null){
                            return;
                        }
 
                        var batchCode      = ((PrimitiveData)fieldData["BatchCode"]).Value;
                        var bundleCode     = ((PrimitiveData)fieldData["BundleCode"]).Value;
                        var boardCount     = ((PrimitiveData)fieldData["BoardCount"]).Value;
                        var boardLength    = ((PrimitiveData)fieldData["BoardLength"]).Value;
                        var boardWidth     = ((PrimitiveData)fieldData["BoardWidth"]).Value;
                        var boardThickness = ((PrimitiveData)fieldData["BoardThickness"]).Value;
 
                        //((PrimitiveData)fieldData["BoardCount"]).Value = 123;
                        //client.Write(endpointDescriptor, nodeDescriptor, attributeData);
                        client.WriteValue(endpointDescriptor, nodeDescriptor, attributeData);
                    }
                }
                catch(UAException uaException){
                    Console.WriteLine("*** Failure: {0}", uaException.GetBaseException().Message);
                }
            }
        }

Exception:
An OPC-UA operation failure with error ID 'Opc.UA.ServiceResult=0x80730000' occurred, originating from 'OpcLabs.EasyOpcUA' and with depth of 1. The inner OPC-UA service exception with service result 'BadWriteNotSupported' contains details about the problem.
 
InnerException:
OPC UA service result - {BadWriteNotSupported}. The server does not support writing the combination of value, status and timestamps provided.
+ A list of parts provided (or not provided) to the Write operation follows. Value: yes, index range: no, source timestamp: yes, server timestamp: yes.
+ When writing, be aware that writing the server timestamp (in this call, 17/08/2021 18:38:28) is not supported by some servers, including the OPC Foundation sample server.
+ The node descriptor used was: NodeId="ns=2;i=6009".
+ The client method called (or event/callback invoked) was 'WriteMultiple'.