When a customer does not pay an invoice by a certain date, that customer might have to pay an additional _____.

A.
sales tax

B.
late fee

C.
installment

D.
discount

B. late fee

To answer this question, we need to understand the concept of invoice payment terms. Invoice payment terms are the agreed-upon conditions between the seller and the customer regarding the payment deadline for the amount due on the invoice.

In this case, when a customer does not pay an invoice by a certain date, they might have to pay an additional amount as a penalty or fee. This additional amount is commonly known as a "late fee" (option B).

To determine the correct answer, we can consider the different options given:

A. Sales tax: Sales tax is a mandatory tax levied on the sale of goods and services. It is not directly related to late payment of an invoice, so it is not the correct answer in this case.

B. Late fee: As explained above, a late fee is an additional amount charged to a customer when they fail to pay an invoice by the specified due date. Therefore, this option is the correct answer.

C. Installment: Installment refers to the division of a payment into smaller, periodic amounts. It does not pertain to late payment penalties, so this option is not the correct answer.

D. Discount: A discount is a reduction in the original price of a product or service. It is not applicable in the context of late payments, so this option is not the correct answer.

In conclusion, the correct answer to the question is B. late fee.