A plugin is missing another plugin it depends on
Applies to Paper, Vanilla.
What it looks like in your log
org.bukkit.plugin.UnknownDependencyException: Unknown/missing dependency plugins: [Vault]
What causes it
A plugin refuses to load because a plugin it depends on is not installed.
How to fix it
Install the missing dependency into the plugins folder and restart. Vault, PlaceholderAPI and ProtocolLib are the usual suspects.
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