This 4-player club has a forum which might answer your question. Or you could post it there.
https://www.chess.com/club/4-player-chess
Four-Player Chess with friends
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Your friends need to be on the https://www.chess.com/4-player-chess page when you invite them.
I have three friends on chess.com that I want to play 4-player chess with, but I can't figure out how to invite them. When I start a game and try to enter their chess.com names to invite them, none of them come up. Any guesses what the issues might be?