Someone - let's call him Bob - contacted me a little more than a year ago to create a solution to automate his business, this solution has been working great for Bob, it makes his job easier and I believe he is making more money with this solution.
Bob is the owner of his business, and I'm the only one who developed and know technically speaking about this solution, the solution is composed of a web app, a mobile app and a connection with two providers.
I charged him initially for building the whole solution, and after that, I charged him for every change I made. For some reason I have never signed a contract with Bob.
I work in a multinational company, which is my 70% - 100% of the total income each month, and also I do some side projects just like the one I made for Bob, but I feel these side projects are taking some days too much time from my free time, and I'm not seeing the amount of money I would like to see exclusively from those side projects.
So I'm starting to charge also a monthly fee/commission on new projects, the benefit for them is that they would not need to pay more if they want an update, the benefit for me is that even if they don't want an update I will get my maintenance fee.
There's no problem with new projects, because we can talk before we work together, but with Bob, we have been working for a year, and it is a deal/client I would not like to lose, because I see potential in this product.
Bob is planning in the long run (I think 3 - 5 years) to start to commercialize this solution and he mentioned one time that he would like me to start making money for this idea too, Bob also once said that he want to make money from a subscription model instead of a one payment only one, he explicitly said that a one-time payment doesn't make sense for him, but a subscription model does.
So, my questions at the end are:
Which is the best way to tell Bob I want to change the way we work together because I want a 10% of the money he is making with this solution each month and not charging him anymore for each change?
Should I mention that he has said in the past that he would like me to make money each month for commercialize this idea?
Should I mention what he said about the subscription and the one-time payment models?