You sold on credit. Then they paid. Which way do you write it? People google debit and credit. In a shop the only question that matters is: does this entry raise what they owe, or bring it down?
Kaymn on kaymn.net has two buttons for that. Receivable means they owe you more — a credit sale, usually. Payable moves the other way: you owe them, or they are paying down what they owed. Recording a payment as another sale is the usual reason it still says they owe 140 after they paid 40 on 100.
Pick one pair of words and stick to it. Don’t keep two lists — “customers” and “clients” — for the same people. See how much they owe.
In Kaymn two buttons and a live balance — 7-day trial.