If the landlord applies for a patent and is authorized to obtain a certificate, he still needs to pay an annual fee to the State Information Bureau, otherwise the patent will be considered invalid. Usually, you need to pay the annual fee before it expires. If it exceeds the time limit, you can pay it back within 6 months (of course, you need to pay a late fee in addition to the annual fee). If the payment is not made for more than 6 months, the patent shall be deemed invalid. The official will generally inform the applicant that the patent right has been terminated.
If you still need to use the patent, you need to submit a patent recovery request to the State Information Bureau. The patentee may, within 2 months from the date of receiving the notice of termination of the right, make a request to restore the right.
Usually, when a patent expires, it forgets to pay the annual fee because the annual fee of each patent is paid at different times.