Multiplayer not working

Had so much hype for the game just to be let down. The game is advertised as a multiplayer dungeon crawler yet you can’t even play with your friend. When i try inviting my friend nothing happens. When i try joining his session it will say the session is full even though it is a private. I found that very disappointing considering the only reason we got the game was for the multiplayer aspect of the game. He plays on a ps5 while i play on the ps4 and no matter what we try and do there is no way we can get into a lobby together. If the game is advertised as a multiplayer game dont you think the multiplayer part of the game works. I play the tutorial and after that was ready to play with my friend just to get disappointed. 30 dollars wasted and for my friend 40 wasted. When will the multiplayer part of the game actually work.