> ## Documentation Index
> Fetch the complete documentation index at: https://devzone.nayax.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Request and Response Format

The Marshall Pro protocol uses a unified JSON structure for every message. This consistency allows you to build a single "wrapper" in your code to handle all terminal communications.

## Request object

Every command sent from your system to the VPOS must follow this structure:

| Field     | Type     | Required | Description                                             |
| :-------- | :------- | :------- | :------------------------------------------------------ |
| command   | `string` | Yes      | The name of the API method (e.g., `"status"`, `"pay"`). |
| requestId | `string` | Yes      | A unique ID used to track the response.                 |
| data      | `object` | No       | A container for the specific parameters of the command. |

### Request example

```json theme={null}
{
  "command": "<command_name>",
  "requestId": "<unique_request_id>",
  "data": {
    "param1": "value1",
    "param2": "value2"
  }
}
```

## Response object

The terminal's response always mirrors your `requestId` so your system knows exactly which command is being answered.

### Success response

If the command is processed successfully, the terminal returns the requested information inside the `data` object.

```json theme={null}
{
  "requestId": "<request_id_echo>",
  "data": {
    "status": "success",
    "details": "..."
  }
}
```

## Error response

If an issue occurs, the response will include an error code and a descriptive message.

```json theme={null}
{
  "requestId": "<request_id_echo>",
  "errorCode": 400,
  "errorMessage": "Invalid command parameters"
}
```