---
title: Errors and troubleshooting
description: Interpret API errors and resolve common Playground failures.
sidebar:
  order: 5
---

| Status | Meaning | Action |
| --- | --- | --- |
| `400` | `month_to` is earlier than `month_from`. | Correct the date range. |
| `401` | The Bearer header is missing, malformed, or invalid. | Verify the header and current key. |
| `422` | A date or `segment` value is missing or invalid. | Use ISO dates and `normal`, `sample`, or `all`. |
| `503` | The external API key is not configured on the service. | Contact Mellow; retrying with another key will not help. |

## Browser reports a CORS error

The live Playground is authorized only from `https://docs.mellow.billgateai.com`. Requests copied into another website or a local HTML page are intentionally blocked by the browser. Use curl or another server-side HTTP client outside the official documentation site.

## The response contains `null`

This is not a transport error. It means that cost is unavailable under the same coverage rules used by the product-profit page. See [Cost semantics](/cost-semantics).