> ## Documentation Index > Fetch the complete documentation index at: https://docs.mx.com/llms.txt > Use this file to discover all available pages before exploring further. # HTTP Status Codes and Errors Error codes and messages are for logging and for informational purposes only and may change from time to time. Do not check for specific codes or messages as this may break your integration. The HTTP status response codes are sufficient for an integration workflow and processing of the error response body is not needed. The Nexus API uses conventional HTTP status codes to indicate success or failure of an API request. In general, codes in the 2XX range indicate success, codes in the 4xx range indicate an error that resulted from the provided information (e.g. a required parameter was missing), and codes in the 5xx range indicate an error with the MX Platform. On success, an `HTTP 200 SUCCESS` will be returned. Most successful `DELETE` requests will return with a status code of `200` and an empty response body, e.g. `{}`. However, certain endpoints — such as delete scheduled payment — return with a status of `204: No Content` without an empty response body. Please pay close attention to the documentation for individual delete endpoints. On failure, a non-2XX HTTP status code will be returned, along with an error response body. Sometimes simply returning the HTTP status code is not enough to indicate what went wrong. To compensate for this, endpoints may respond with a body containing more information about the error. An error response body consists of a code and a message. * A `422` error with a `4220` code can occur on a create member request for the following reasons: * The user already has a member connecting it to the same institution, using the same login credential. The duplicate member is not allowed. * The provided `external_guid` value already exists in a member belonging to a user in the same client. Please use a unique value. * The provided `institution_guid` does not exist. | Error Code | HTTP Status Code | Status | Error Description | | :--------- | :--------------- | :-------------------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `4001` | 400 | Bad Request | Required params missing. | | `4002` | 400 | Bad Request | One or more parameters were not permitted. | | `4003` | 400 | Bad Request | Cannot create/update goal. Monthly Contribution from the MonthlyCashFlowProfile must be greater than 0. | | null | 400 | Bad Request | The date range provided was invalid. | | null | 400 | Bad Request | Monthly Cash Flow Profile is invalid. | | null | 400 | Bad Request | A submitted parameter field is invalid. | | null | 400 | Bad Request | You cannot aggregate a manual member. | | null | 400 | Bad Request | Account guid is not valid. | | `4011` | 401 | Unauthorized | The session token used in this request has expired. | | null | 401 | Unauthorized | Invalid API token. | | null | 403 | Forbidden | Operation is forbidden. | | null | 404 | Not Found | We were unable to find the record you requested. | | null | 405 | Method Not Allowed | Method not allowed. | | null | 406 | Not Acceptable | The request cannot be accepted. A required header may be missing or invalid. | | `4220` | 422 | Unprocessable Entity | Record could not be saved. See note below. | | `4221` | 422 | Unprocessable Entity | When attempting to auto-generate budgets, no category contained the minimum required number of transactions. See the auto-generate budget endpoint for additional information. | | `4230` | 422 | Unprocessable Entity | Institution is unavailable or blocked. See [Institution Blocking Errors](#institution-blocking-errors). | | null | 422 | Unprocessable Entity | Record could not be saved. One or more parameters is invalid. | | null | 429 | Too Many Requests | This error is triggered when exceeding the maximum number of concurrent connections or rate limit. See details below. | | null | 500 | Internal Server Error | An unknown error has occurred. | | null | 404 | Not Found | Challenge question expired. Please try again. | | null | 400 | Bad Request | The credential GUIDs submitted are no longer valid. Check the institution required credentials endpoint for the most recent credentials. | ### 429 Too Many Requests This error is triggered when exceeding the maximum number of concurrent connections, or the rate limit for requests per second (rps) is surpassed. Requests receiving a 429 status code should be retried once the rate limit window has expired. To prevent this error, decrease the number of concurrent connections or the number of requests per second. Rate limiting is applied per client with the following thresholds: * GETs: 2000/rps * POSTs: 750/rps * PUTs: 750/rps * DELETEs: 150/rps Individual features may implement specific rate limit overrides. ## Institution Blocking Errors Member operations (create, update) and job creation (verify, identify) may be blocked based on an institution's `status` or `client_status` fields. When blocked, the API returns a `422 Unprocessable Entity` error with a user-friendly message. ### Error Response Structure ```json theme={null} { "error": { "code": 4230, "message": "This institution is temporarily unavailable due to scheduled system maintenance. Access will resume once maintenance is complete. Please try again later.", "status": "unprocessable_entity" } } ``` The `error.message` field contains text that can be displayed directly to end users. The specific message depends on the institution's `status` or `client_status`. ### Common Blocking Scenarios | Scenario | HTTP Status | error.code | error.message | | -------------------------- | ----------- | ---------- | --------------------------------------------------------------------------------------------------------------------------------------------------------- | | Institution in maintenance | 422 | 4230 | This institution is temporarily unavailable due to scheduled system maintenance. Access will resume once maintenance is complete. Please try again later. | | Institution unavailable | 422 | 4230 | This institution is experiencing technical issues that are preventing successful connections. It's unclear when this will be resolved. | | Data not available | 422 | 4230 | The requested data isn't available through this institution. | | New connections blocked | 422 | 4230 | This institution is not available for connection. | | Verification blocked | 422 | 4230 | The requested data isn't available through this connection. | ### Best Practices * When you receive a 422 error with code 4230 for member operations, the error is institution-related * Display `error.message` to users as it provides clear, user-friendly explanations * Provide clear feedback to users about why the operation failed due to institution unavailability or restrictions