In version 7.75 and above, payments are distributed based on the Business rule option selected in Configuration. If the option selected is to distribute payments proportionally based on the balance, the amount applied to each record will affect the charges and age of the charges paid by the payment.

To resolve this issue, when entering payments, on the Student Billing Detail tab, select to Delete All which will remove the distribution of the payment between records and pay off the oldest transactions for which the payer is responsible.