The installer was launched instead of the server
What it looks like in your log
java.awt.HeadlessException at net.minecraftforge.installer.SimpleInstaller.main
What causes it
The Forge or NeoForge installer jar was set as the start jar. It tries to open a window, which a server box does not have.
How to fix it
Run the installer once with --installServer, then point the start command at the generated run script, not the installer 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