That file is not a runnable server
What it looks like in your log
no main manifest attribute, in server.jar
What causes it
The selected file is not a valid Minecraft server jar.
How to fix it
Check you picked the right server jar (for example server.jar, or the pack’s start jar).
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log