What are the consequences of not paying the annual patent fee?

If the applicant fails to pay the application fee (including document printing fee, specification and claim surcharge) within two months from the date of filing, his patent application shall be deemed to have been withdrawn.

Although the applicant has paid the application fee, but the formalities are improper, such as the items listed in the payment form are incomplete or incorrect, or the payment form is not attached, which leads to the suspension or refund of the payment, it is regarded as unpaid, and the Patent Office will treat it as unpaid application fee.