I bought Halo masterchief collection and tried to access nightfall last week but said i had to buy it, but i contacted microsoft and they said i should have got a code with it but i didnt, so said to come on here and post for yous to sort out a code for it .
Did you buy a phisical copy or a digital copy? If it was physical then yes there should have been a code. If you don’t have one, you would need to speak to the store you bought the game from. If you bought digital, have a read thtough this troubleshooting thread from the Forum Team