Yes. 4xx codes are client errors: The request contains a mistake or can't be fulfilled as sent.

4xx · Client error

HTTP 423 Locked

The resource is locked (WebDAV).

Example response

HTTP

HTTP/1.1 423 Locked
Content-Type: application/json; charset=utf-8

{ "error": "Locked" }

Look up the headers shown here in the HTTP headers reference.

What does HTTP 423 mean?: Locked. The resource is locked (WebDAV).
Is 423 an error?: Yes. 4xx codes are client errors: The request contains a mistake or can't be fulfilled as sent.