What is the simplest wordpress order tracking system you can recommend?

Question

WordPress

Essence:
There is me and there is a customer. A person transfers money to me, I make a note on the site, my customer sees this note if he logs into the site.
Why do I need this:
In order not to look at the transaction every time and remember when this transaction has happened. And so that the user himself could look clearly and not mislead me after a couple of days when this transaction occurred.
In fact, no bindings to payment or other systems are needed, such notes, maybe Handcrafted invoices. Purely for your personal account and visual proof to users.