# SINGLETON_BLOCKED: The type cannot be a singleton on this ref

> A singleton type has one entry, under its own slug, and this ref holds more than that, a subtype, or its one entry under another slug. The detail names what is in the way.

Sent by the management API (400). The page: https://coho-cms.com/errors/singleton-blocked/

## What to do

Remove or move what the detail names, then make the type a singleton.

## The response

```json
{
  "code": "SINGLETON_BLOCKED",
  "type": "https://coho-cms.com/errors/singleton-blocked",
  "title": "The type cannot be a singleton on this ref",
  "status": 400,
  "detail": "What went wrong in this request, in a sentence.",
  "instance": "/v1/projects/…"
}
```

Every error code: https://coho-cms.com/errors/