communication from xbox 360 to xbox one

You may be right. I haven't played a backwards compatible game in a while.

I thought to get the 360 menu on the XBox1 while in a 360 game was by pressing the 2 buttons below the Nexus button simultaneously.

From there choose mail and accept friend request etc

The friend system is different on the 360 than on the One. The One has a follower system instead of friend system. You may want to try using the Xbox app to see if you can add them through there or if they start a 360 game on their console and press the
Xbox button to pull up the 360's menu they may be able to accept your request there.

Adding a friend should work regardless of console. You can try to do it on the Xbox website if necessary.

Be aware however, that the Xbox 360 has a friend list limit of 100, so if you already have that many people on your friend list, you can't add that person as a friend.

Also, sending a friend request to the Xbox One doesn't show up as a "friend request". Instead, you automatically become a "follower" of that Xbox One user. Only when the Xbox One user friends you back, you are actually friends.

Also be aware, that you can't communicate from Xbox 360 to Xbox One, UNLESS the Xbox One user is playing a Xbox 360 backwards compatible game.

However, you can still use the Xbox app on a Windows 10 PC to participate in a party-chat with Xbox One users, without them being in a Xbox 360 game.

I just found out you can join Xbox LIVE parties with people from Xbox 360 & Xbox One and talk

www.polygon.com/.../xbox-live-accounts-compatible-across-xbox-one-360-communicate-chat