https://en.wikipedia.org/w/api.php?action=query&list=categorymembers&cmtitle=Category:WikiProject_Democratic_Republic_of_the_Congo_articles&cmlimit=max seems to work fine.

If i were to guess why its not on list=projectpages, id say that wikiproject democratic republic of the congo is not a full on wikiproject itself but just a subproject of wikiproject africa.

--
brian

On Saturday, February 17, 2018, Bowen Yu <bowen-yu@umn.edu> wrote:
> Hi, 
> I am trying to get articles belong to WikiProject Democratic Republic of the Congo. I tried both API calls and Quarry (I guess they shared the same data source), but did not get any articles back. I wonder if anyone has any sense what's going for this project in the database? I just used "Democratic Republic of the Congo" as the query input. Thank you!