Hello @chi1989
If the datasets are inside a collection, downloading that collection directly is currently problematic at UseGalaxy.org.
A workaround using the “history archive” method is in this Galaxy Help topic: Problems in downloading collections using both browser and curl - #4 by jennaj
But if it really is just a single paired collection (two datasets), you could also go into the hidden datasets tab for the history, and download the two datasets from there.
Hope one of those work out for you!