changelog entry

CHANGELOG.md

@@ -29,6 +29,7 @@ Unreleased changes are available as `avenga/couper:edge` container.
   * Request methods are treated case-insensitively when comparing them to methods in the `allowed_methods` attribute of [`api`](./docs/REFERENCE.md#api-block) or [`endpoint`](./docs/REFERENCE.md#endpoint-block) blocks ([#478](https://github.com/avenga/couper/pull/478))
   * Do not allow multiple `backend` blocks in `proxy` and `request` blocks ([#483](https://github.com/avenga/couper/pull/483))
   * Panic if an [`error_handler` block](./docs/REFERENCE.md#error-handler-block) following another `error_handler` block has no label ([#486](https://github.com/avenga/couper/pull/486))
+  * Invalid (by [OpenAPI validation](./docs/REFERENCE.md#openapi-block)) backend response missing in [`backend_responses`](./docs/REFERENCE.md#backend_responses) ([#501](https://github.com/avenga/couper/pull/501))
 
 * **Removed**
   * support for `beta_oidc` block (use [`oidc` block](./docs/REFERENCE.md#oidc-block) instead) ([#475](https://github.com/avenga/couper/pull/475))