On Halo Reach I did the challenge “ENDURE: THE RETURN” which is to "Complete four sets on any Firefight map in co-op play on Heroic or harder. Its worth 30000 cR. And I did exactly that. I played 4 set’s on firefight and firefight classic with my friend on local on Corvette on Heroic. I didn’t get the credits even though I played it twice. Please help so those 5 hours wasn’t for nothing
You may need to complete that challenge in the Online Firefight playlist, as very few challenges can be done local (excluding campaign).