Why does the system not allowing to alter the direct payments and show message ‘ Transaction is already Paid’?

Suggestions:
Direct Payments is a payment entry indicating that payment has been made for a Purchase receipt or any other payments.
However when the paymnet is made, when user click on paid option, the system will not allow the user to alter the record. System shows the message as ‘ Transaction is already Paid’, ‘ Edit is not allowed for already Paid Transaction’. Alteration of the direct payment record can be done before its paid off.