Can you paste the error here? Is it in the server log? Have you tried with a template project? If you follow these steps with a template project you’ll be able to play on a dedicated server.
I have noticed that things are different in the standalone dedicated server vs. PIE, so part of my dev iteration includes deploying the dedicated server and testing against it. There will be warnings, errors, and behaviors I haven’t seen in PIE that need remedying.
I’m curious if some of your game’s content wasn’t cooked / isn’t available to the server. I assume it is available to the client – are you seeing things correctly before connecting to your dedicated server instance?