# Invalid content entry slug.

> `COLLECTION_NAME` → `ENTRY_ID` has an invalid slug. `slug` must be a string.

## What went wrong?

[Section titled “What went wrong?”](#what-went-wrong)

A collection entry has an invalid `slug`. This field is reserved for generating entry slugs, and must be a string when present.

**See Also:**

* [The reserved entry `slug` field](/en/guides/content-collections/)