API
Any API
Two systems share one record, and a failed sync shows itself.
An API here is the pipe between the desk you already run and the next tool that needs the same number.
A sale, a fee, a delivery, or a stock count is typed once. The other screen reads it.
We start by naming which system owns the number. The shop, the accounts book, and the branch do not all get to invent a total.
Each call has a name a person can say. Staff do not have to learn a vendor's private language.
When a call fails, the desk shows the row, the time, and the reason. A silent gap is not an acceptable morning.
Retries are visible. A person can send the row again or hold it when the other side is down.
Keys and passwords stay off the page. The public site never prints a connection string.
A new branch, a new shop, or a bank feed can be added later without rewriting the first desk.
The first screen is a map: what leaves, what arrives, and who is told when it does not.
You see that map before the full connection is written, while it is still cheap to change the shape.