Well there’s a link on the github page to the API web site: fortniteapi.com
Going to that site gives me:
"Fortnite API is now back as Mative
Try us out, it’s free :)!
Going to the link in that page -> “Coming soon”
So I guess the conclusion is the API has gone down. Maybe there’s another API that can be used. I haven’t researched it, but be free to do so