Why won't my server start?
Short answerOpen the Console and read the last lines before it stopped; the error almost always names the cause. The most common ones are a plugin or mod that does not fit the Minecraft version, too little memory for a modpack, and a broken file after a change.
Find what stops it
Open the Console and start the server. Watch the output until it stops.
Scroll up from the last line to the first line that says ERROR or Exception. The lines under it usually name a plugin, a mod or a file.
Did it start right after you added or updated something? Remove that plugin or mod on its tab and start again.
Still stuck? Restore the backup from before the change, or send us the console lines.
What the common errors mean
"OutOfMemoryError": the server needs more memory than your plan has. Usually a modpack that is too big for the plan, or a memory leak in a plugin.
"Unsupported class file" or a plugin that says it needs another version: a plugin or mod that was made for a different Minecraft version.
A line naming a file with "could not parse" or "malformed": a settings file with a typo, often after editing it by hand. Undo the edit or restore the file from a backup.
Let the Copilot read it
The AI Copilot in your panel reads the same logs and can point at the line that matters and propose a fix, which you apply yourself.
Questions people also ask
What should I send support?
The server name, the console lines around the first error, and what you changed just before it stopped starting. With those we can usually tell you the cause in one reply.