HTTP 418 I'm a Teapot was defined as an April Fools' joke in RFC 2324 (Hyper Text Coffee Pot Control Protocol). It indicates that the server refuses to brew coffee because it is permanently a teapot. Some servers implement this as an easter egg.
The server intentionally returns 418 as a humorous response, often on specific endpoints.
Some servers return 418 to bots and scrapers as a non-standard block response.
You may be hitting an easter egg endpoint. Verify you are requesting the correct URL.
If you are making automated requests, the server may be using 418 to block bots. Add a proper User-Agent header.