Almost every small landlord in Kenya starts with a receipt book. It works, it costs a few hundred shillings, and it is what everyone else does. The cost shows up later, and not where you expect.
The dispute you cannot settle
A tenant says they paid for March. You think they did not. The receipt book says nothing useful, because the carbon copy is illegible or the book from that quarter is in a drawer somewhere.
Whoever is more insistent wins that argument. That is not a good way to run a business, and it is not a good way to keep a tenant either.
The reconciliation you cannot do
At the end of the year you want one number: what should have come in, and what actually did. With a receipt book you have a stack of paper in no particular order, and the only honest way to get that number is to sit down for an afternoon with a calculator.
Most landlords do not do this. They estimate, and the estimate is generous.
The pattern you cannot see