Add additional columns azure data factory

Question

Operation on target CopyFromBlobToSQL failed: ErrorCode=AdditionalColumnWithInvalidDataset,'Type=Microsoft.DataTransfer.Common.Shared.HybridDeliveryException,Message=Additional column doesn't apply for current dataset.,Source=Microsoft.DataTransfer.TransferTask,'

        PipelineResource pipeline = new PipelineResource
        {
            Activities = new List<Activity>
            {
                new CopyActivity
                {
                Name = "CopyFromBlobToSQL",
                Inputs = new List<DatasetReference>
                {
                new DatasetReference() { ReferenceName = _blobDatasetName}

                },
                Outputs = new List<DatasetReference>
                {
                new DatasetReference { ReferenceName = _sqlDatasetName }
                },
                Source = new BlobSource { AdditionalProperties = addColumns },
                Sink = new SqlSink { },

            },                  
            },
        };

        Dictionary<string, object> addColumns =
new Dictionary<string, object>();
        addColumns.Add("additionalColumns", new object[] {

            new AdditionalColumns(){Name = "ProjectId", Value ="123"}

        });