I will like to add to the above and give some practical insights based on how I established my proof of concept -
Before that, first - how you plan to make money? As in is the business model geared towards acquiring users first and then monetizing or doing a trial to conversion or transaction based selling etc. Depending upon your business, you will know well which one suits at-least the initial hypothesis.
So once you have the hypothesis, the first step, research your target audience -
1. Where they engage online?
2. What they might search in Google?
If you are able to do the above, then just create 2-3 landing page testing one value proposition each - you will be able to set this up in unbounce.com, leadpages, tons of them available. Most of them give 30 day trial for the pro plans.
Run basic ads - and see if you are able to attract some initial leads.
Then try to get some detailed insights from people who have shown interest and ask them what will they pay (the pay is again based on what your model is, if it is users, you don't need to even go to the money talks)
Based on this, get the business plan done and start pitching.
This will show that you have done some ground work and understand some insights.