protected function getApiHeaders(): array
    {
        $headers = [
            'Accept' => "application/vnd.KATSANA.{$this->getVersion()}+json",
            'Time-Zone' => $this->requestHeaderTimezoneCode ?? 'UTC',
        ];

        if (! \is_null($accessToken = $this->client->getAccessToken())) {
            $headers['Authorization'] = "Bearer {$accessToken}";
        }

        return $headers;
    }