Charging clients per order executed.. possible?

As per article: https://techcrunch.com/2019/11/08/alpaca-stock-trading-api/
It portrays the service as “creating your own robinhood”…
If we decide to create an application integrated with Alpaca… are we able to charge clients fee per trade execution?

How will that look programmatically?
How does one capitalize on creating an application and charging end users?