I watched all 5 episodes of halo nighfall and i didnt unlocked the nighfall armor on halo 5, i repeat the episode a bounch of times, but i still didnt get the reward on halo channel, i got the movie by a code on the MCC copy, is that the problem?
The code is alright. The problem is the Halo channel app, which is extremely buggy and may not count the episodes you watched. Try to watch the side stories of every episode.
Nightfall armor can also be unlocked through Halo 5 gold req packs.