I have been working with PHP for over 18 years, so throughout the years I'd met a bunch of different PHP developers, but I was beginning to exhaust my list of folks that had kept with it and were distributing their packages online (free or paid).
So, I decided to reach out to several sellers on places like CodeCanyon and similar marketplaces. There has been a decent bit of displeasure with the way that ThemeForest and similar websites handle their commission structure and how they own their entire developer base's brands and traffic. Aha! A new angle.
I then began to ask these users the same questions as before, but I added in the emphasis that you would retain all of your customer data, could create email lists, and get churn notifications all in the product (I was already adding these features to the roadmap).
As a result, I got another 5 users. So I was just one short.
The one thing I hadn't done yet is what everyone always says to do... ask people you know.
I have a colleague that constantly makes composer packages and was interested in the idea from the start. I reached out to him and he was the 10th one I needed.
Obviously I'll continue to do some customer research and validation, but at this point I was sure that there was a need for the product.