There's no "platform fee" per se, for using Lightspeed Trader.
To be clear, there are market data fees which can vary depending upon which marketplaces you wish to subscribe to, and whether you're categorized by the exchanges as a "professional" or "non - professional". These market data fees are charged by the exchanges themselves and Lightspeed simply passes along such charges to those traders incurring them.
There are also execution fees that are charged by the venues themselves for removing/adding liquidity, depending upon the scenario. These too are not Lightspeed fees, and like many firms, we post a schedule of such on our web site.
I hope this is clear enough.