> For the complete documentation index, see [llms.txt](https://developer.esw.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.esw.com/returns-api/grp-returns-api/error-handling/error-schemas.md).

# Error Schemas

This API uses three error schemas. Two share the same field shape but are registered under different names in the spec. Always check which one is returned for a given endpoint and status code.

#### Schema 1 — `ProblemDetails`

Used for: `401`, `403`, `404`, `409`, `500` on most endpoints. Two aliases exist — `Microsoft.AspNetCore.Mvc.ProblemDetails` and `ProblemDetails` — both have identical structure.

```json
{
  "type": "string",
  "title": "string",
  "status": 401,
  "detail": "string",
  "instance": "string"
}
```

All fields nullable. `additionalProperties: {}` — extra fields may appear.

#### Schema 2 — `ValidationProblemDetails`

Used for: `400 Bad Request` on all endpoints that document it. Two aliases — `Microsoft.AspNetCore.Mvc.ValidationProblemDetails` and `ValidationProblemDetails` — both identical.

```json
{
  "errors": {
    "FieldName": ["Error message one.", "Error message two."],
    "nested.Field": ["Error message."]
  },
  "type": "string",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "detail": "string",
  "instance": "string"
}
```

The `errors` object is a **dictionary mapping field names to arrays of error strings**. This is not a flat array. Iterate the dictionary keys to read every validation message. All top-level fields nullable. `additionalProperties: {}`.

#### Schema 3 — `BaseResponse`

Used **only** for `500` on `GET /{identifier}/return-orders/{returnOrderNumber}/{documentType}`.

```json
{
  "userMessage": "string",
  "details": "string"
}
```

`additionalProperties: false` — no extra fields. This schema surfaces user-readable error detail, unlike the more technical `ProblemDetails`.

#### Universal Safe Parser

{% code expandable="true" %}

```javascript
async function parseGrpError(response) {
  const text = await response.text().catch(() => "");
  if (!text.trim()) {
    return { schema: "none", status: response.status };
  }

  let parsed;
  try {
    parsed = JSON.parse(text);
  } catch {
    return { schema: "unparseable", status: response.status, raw: text };
  }

  // BaseResponse: has userMessage/details, no title
  if ("userMessage" in parsed && !("title" in parsed)) {
    return {
      schema: "BaseResponse",
      status: response.status,
      userMessage: parsed.userMessage ?? null,
      details: parsed.details ?? null,
    };
  }

  // ValidationProblemDetails: has errors dict
  if ("errors" in parsed) {
    return {
      schema: "ValidationProblemDetails",
      status: response.status,
      errors: parsed.errors ?? {},
      title: parsed.title ?? null,
      detail: parsed.detail ?? null,
      type: parsed.type ?? null,
      instance: parsed.instance ?? null,
    };
  }

  // ProblemDetails
  return {
    schema: "ProblemDetails",
    status: response.status,
    title: parsed.title ?? null,
    detail: parsed.detail ?? null,
    type: parsed.type ?? null,
    instance: parsed.instance ?? null,
  };
}
```

{% endcode %}


---

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