"Skill not found" is the most common skill error. It means the CLI tool that the skill depends on isn't in your system PATH. Every skill has a SKILL.md file that lists its requirements. Read it.
To check which skills can run on your machine right now, use openclaw skills list. For only the ones that pass all checks, use openclaw skills list --eligible.
There's a bug you should watch for. Issue #9469 causes skills to show as enabled in your config but be disabled at runtime. You won't get an error. The skill just silently won't trigger. If a skill isn't firing when it should, run openclaw doctor --fix to reconcile the config with the runtime state.