Hi
Since I dont have your data etc please try this
SortByColumns(Distinct(
Filter(
Tables;
ClientName = drpDown.Selected.Value
);
ArticleReference
), "ArticleReference", SortOrder.Ascending)
If the "ArticleReference" gives you an error, try "Value" instead
Lastly, I have it sorting Ascending, you may want it Descending, not sure based on your Dataverse Sort. Also, don't assume the sort order in Dataverse is what you see or need, its not doing by your column.
Cheers,