# EPUBCheck OPF-030: The unique-identifier … was not found

Source: https://epublab.com/epubcheck/opf-030/ (updated 2026-11-03)

EPUBCheck OPF-030 is an error message: “The unique-identifier "…" was not found.” The package element's unique-identifier attribute names an id that no dc:identifier element has.

- Official message (EPUBCheck 5.4.0): The unique-identifier "%1$s" was not found.
- Default severity: Error

## Typical causes

- The id on dc:identifier was renamed or removed, for example when editing metadata by hand.

## How to fix it

- Make the id on one dc:identifier match the unique-identifier attribute, for example <package unique-identifier="uid"> with <dc:identifier id="uid">urn:uuid:…</dc:identifier>.

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EPUBLab.