Documentation edits made through Mintlify web editor

Author: tcaldwell-x

x-api/fundamentals/response-codes-and-errors.mdx

@@ -23,6 +23,7 @@ Error responses are served with a non-200-series HTTP code. Different error code
 | 409 | Connection Exception | Returned when attempting to connect to a filtered stream that has no rules. | Check that you have created at least one rule on the stream you are connecting to. Filtered stream will only return Posts that match an active rule. If there are no rules, the stream will not return any Posts. |
 | 429 | Too Many Requests | Returned when a request cannot be served due to the App's [rate limit](/resources/fundamentals/rate-limits) or [Post cap](/x-api/fundamentals/post-cap) having been exhausted. See [Rate Limiting](/resources/fundamentals/rate-limits). | Check the number of requests per timeframe allowed with the endpoint you’re using. Wait for the timeframe to reset. Space out your requests to ensure you don’t hit rate limits or upgrade to the next available data plan. |
 | 500 | Internal Server Error | Something is broken. This is usually a temporary error, for example in a high load situation or if an endpoint is temporarily having issues. | Check the X API [status page](/status) or the [developer community forum](https://devcommunity.x.com/) in case others are having similar issues, or simply wait and try again later. |
+| 501 | Unimplemented | The X API does not support this endpoint and cannot fulfill the request. |  |
 | 503 | Service Unavailable | The X servers are up, but overloaded with requests. Try again later. | Check the X API [status page](/status) or the [developer community forum](https://devcommunity.x.com/) in case others are having similar issues, or simply wait and try again later. |
 
 When an error is incurred during a request, detailed information about the error is returned in the response body to aid in diagnosing the problem. A type field, which is a URI, indicates the nature of the problem, while additional fields provide details about the problem. The type, title, and detail fields will always be returned in these bodies (see table below). Any additional fields, as in the example below, will vary depending on the type of the error.