an XDataWebDataSet is bound to a WebDBGrid. An append of the XDataWebDataSet always inserts a row in the grid but not at the end.
Although the dataset is sorted
XDataWebDatasetPOS.QueryString := '$filter=(F_ID%20eq%20'+QuotedStr(IntToStr(F_ID))+')'+'&$orderby=lfdNr'
I retested this here with the demo under Demo\Basics\DBGrid with added code:
procedure TForm1.WebButton1Click(Sender: TObject);
begin
webclientdataset1.Append;
webclientdataset1.FieldByName('Brand').AsString := 'Tesla';
webclientdataset1.Post;
end;
and it always adds the record at the end here