public function getClient(): SellsyClient
    {
        if (!$this->client instanceof SellsyClient) {
            $this->client = new SellsyClient(
                $this->getTransport(),
                $this->apiUrl,
                $this->oauthAccessToken,
                $this->oauthAccessTokenSecret,
                $this->oauthConsumerKey,
                $this->oauthConsumerSecret
            );
        }

        return $this->client;
    }