Can't add teammates to fireteam / friends list?

Ive been playing the game with some friends so far, and having some trouble. My friends and I like the game, but whenever we run into someone in a lobby that we liked playing with, we can’t invite them to our friends list or invite them to our fireteam? For example, we recently played with someone who co-piloted a warthog with us for a whole game. We really wanted to invite them to our fireteam to play more, but there’s no button on the profile to add them to our friends list, send them a message, or even communicate with them at all. It seems like there’s no way in game to even group up with other players that you don’t already know from steam or discord? Really frustrating.