Debtor and related processes in practice
The other party debt situation (the one who lends) is called a creditor. The borrower has a debt to the creditor and the creditor has a claim against the debtor. The relationship between them is covered by the agreement. The agreement usually contains the subject of the loan and a due date.
It is important to have sanctions in the agreement against the debtor in order to have some leverage if the borrower fails to pay.
In practice (not unusual in common practice) the customer can be delayed in payment for purchased goods or services. In this case, the dunning process follows. If that does not work, then you can apply sanctions against the debtor or to start an enforcement processes.