func writeErrorResponse(ctx context.Context, w http.ResponseWriter, err APIError, reqURL *url.URL) {
	if err.HTTPStatusCode == http.StatusServiceUnavailable {
		// Set retry-after header to indicate user-agents to retry request after 120secs.
		// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After
		w.Header().Set(xhttp.RetryAfter, "120")
	}

	switch err.Code {
	case "InvalidRegion":