Custom game issues... Help!!

I’m having issues Making a custom game in halo Mcc , whenever I have the option for the second controller to join the game to “press a to join” it allows me to select guest but doesn’t add the second controller to the game… I’ve made sure both controllers are synced and working (I tried both individually in campaign mode) I also made sure both controllers were updated , I also hard rebooted my Xbox … ANY ADVICE???