Error codes
Every error the CLI prints has a code like MFEFLOW_E102, a cause, a fix and a link to a page. This page lists them all. The first digit is the area, and it sets the exit code. Messages that start with MFE_ come from the browser runtime. Those are covered in Troubleshooting.
Project and config (E1xx, exit code 3)
Features (E2xx, exit code 4)
Build and runtime (E3xx, exit code 5)
Registry (E4xx, exit code 6)
E107 and E215 are command-line mistakes and exit with code 2. The E5xx range belongs to deploy, promote, rollback and status and exits with code 7: