On a listen server you are the client and the server.
Your Projectile needs to have Replicates AND Replicates Movement ticked.
On Fire pressed should check who’s calling it. Client or Server. You can use Switch has authority to do so.
Input pressed: switch has auth[remote] → Call server event [runs on server]
server event: switch has auth[Auth] → spawn the projectile etc etc.
see the following post for BP: [HELP] Multiplayer projectile replication - #13 by Rev0verDrive