I'm not familiar with that issue, but according to the interwebs, it has something to do with the party feature. You can do it through RLLobby, or if you trust your friend, direct IP and port forwarding

Hello,
I recently tried to host a game through the bakkesmod and run this escape room with a friend [this was attempted on the day of this comment being submitted]. I tried launching a game through the Rocket Plugin while he was in my party as that said it would auto-invite him, but then it fed him back an error that steam servers failed to authenticate. Both of us have the steam version of Rocket League. I'm hoping I can get some help, unfortunately none of the fixes I researched and tried worked.

Netcode is back! The map will work as usual now

Ok, ty for the support, nice map btw

There's an issue with netcode right now. So until it gets updated, any map that uses it will crash the game

What to do if the second player crash everytime ? The host does not have this problem

Seems like the numbered balls broke for us, we were missing a ball with a 9 on it.

We tried it and got stuck on the second room (with the coloured goals) as we just couldn't get a ball in the room, for us to score a goal. Is it broken or have we missed something? Felt like we tried everything

Make Sure to download Netcode. A lot of people have this issue. Read "NEEDED BEFORE STARTING"

bruh the symbols are not visible on my screen. what to do

This happens if one player doesn't have netcode. Read "Needed Before Starting"

We dont see the first message in the first room.
The second player cant tell the first player which symbol are the once he need to read.