# API Request/Response Common Elements and Headers
source: https://developer.mastercard.com/mdes-pre-digitization/documentation/api-basics/common_elements_headers/index.md

Every inbound and outbound request contains an element requestId that uniquely identifies the request. Every response contains an element responseId that uniquely identifies the response. The responseId may optionally use the corresponding requestId. Note that the format and uniqueness of the requestId and responseId are not validated.

In case of an operation reporting an error, the response (or an object within the response) contains the element 'errorCode' and optionally the element 'errorDescription', as defined in the Error Codes. Unless explicitly stated otherwise, no other element (including 'Required' fields) is preset to "NONE" and error is reported.

The error elements can be returned in the response for any of the API calls.

## Common Request Elements {#common-request-elements}

|                                   Parameter                                    | Required | Example |
|--------------------------------------------------------------------------------|----------|---------|
| requestId - Unique identifier for the request. Max length - 64. Type - String. | Yes      | 123456  |

## Common Response Elements {#common-response-elements}

|                                               Parameter                                               |                             Required                              |              Example              |
|-------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------|-----------------------------------|
| responseId - Unique identifier for the response. Max length - 64. Type - String.                      | Yes                                                               | 123456                            |
| errorCode - Error Code for the reason the operation failed. Max length -32. Type-String.              | Conditional-required if an error occurred performig the operation | INVALID_JSON                      |
| errorDescription - Error description of the reason the operation failed. Max length-256. Type-String. | No                                                                | JSON Validation failed formatting |