Best way to show potential profitability for a start up social media app intended for retailers and shoppers?

I have a very early early early start up app that isn’t necessarily a retail product. It’s more of a SaaS product, or a social media app that SMB, Mid Market, or even Larger retailers would be able to use to market and sell their products, meanwhile regular users would be able to go on just to check them out and purchase etc. there are a couple unique propositions about it that I won’t mention for right now just for privacy purposes. My main question is, how can you best identify the profitability of what an app will do if it’s not directly based on units sold initially? Maybe it’s on the amount of retailers that sign up and pay a subscription to market their products on the app, etc.. Any ideas I appreciate you all and I’m fairly new to this so take it a little easier on me 😂