Still can't play co-op or add anyone to the roster

Games Halo: The Master Chief Collection
1

tried playing a game with my cousin last night but still nothing it still says 1/16 players even though he accepted my invite

2

Here are a few things to try. I put them in order of least annoying to most annoying so you can pick through them one at a time.

  1. try joining an XBL chat party with him. If this does not work unplug your xbox for 10 seconds and then restart it
  2. unplug your modem for 30 seconds and plug it back in. if you are using a wireless router do the same with this as well.
  3. Set a static IP address in your system settings
  4. Open up your NAT
  5. reflash your firmware on your modem.
3

Go to Settings -> Network

Ensure that it does not state Strict, Strict NAT can cause many connectivity issues as it did for me