Would you sell a $1200 MRR business for $28000

Revenue is a good starting point to evaluate a business when you are talking about companies that grow fast, usually, in a winner take all market (Uber, Spotify, Amazon). In your case, it is not.

Considering the fact that the market is stable and so is your growth, profit is the measure you should look at in your case. I would ask for at least 5x your annual profits.

if revenue == stable && need != money
return NO

How much money would need to be invested in public markets to get a safe $1200/month return?

I think what you have is more valuable than the 2x earnings that you are being offered. Semi-passive income is a pretty great in my opinion.

I’m not sure what your maintenance tasks are on a monthly basis, but that could potentially be outsourced for a low cost.

However if you have a successful or high potential main project, sometimes unloading a distraction might be the right move.

Nope i won't sell
I will ask the existing customer and improve the app on a long term bases and improve is slowly and steady.

2x ARR for a business that is not growing is not great but not terrible either. The question really just boils down to whether you would like 2 years of returns right now or not. Whether you take the deal I think mostly comes down to how much you need the money, or whether you really hate operating the business.

Have you got an offer for $28K? If not, it might still be difficult to get one and you are either stuck with the choice of running the business or closing it down.

3-4 hours per month doesn't seem like much at first but is it realistic. What about customer support? It might still be very disruptive to your work day to have to respond to inquiries. What about filling taxes every year, etc.? That could easily be more than 3-4h per month in Q1 each year.

After that is how niche is the product? Is competition in the space bound to be heating up and then, churn quicks in and you are suck into investing into product/marketing efforts just to keep up the same revenue.

Is the product somehow tied to other products you are working on? It might not make much money but a good way to create a lead and/or value-add channel.

which business is it sir