Final answer:
A certifying officer becomes liable when an improper payment is made due to their erroneous certification, which means they are responsible for correcting the mistake.
Step-by-step explanation:
The certifying officer is liable from the moment an improper payment is made as the result of his or her erroneous certification. When a certifying officer erroneously certifies a payment, they are held accountable for that mistake. This liability means that the officer can be subject to financial restitution towards correcting the improper payment. The concept of liability ensures that certifying officers perform their duties with due diligence to prevent such errors.