Is it illegal to sell patents without paying patent fees? Can you still sell it?

The annual patent fee refers to the fee that the patentee shall pay to the Patent Office year by year from the year when the patent right is granted. The annual fee for the year when the patent right is granted shall be paid within the time limit specified in the notice of granting the patent right issued by the Patent Office, and the annual fees for subsequent years shall be paid in advance within one month before the expiration of the previous year. If the payment is not made within one month before the expiration, the Patent Office will grant a grace period of one month. If the fee is not paid within one month after the expiration, there will be a late fee. If it can't be sold, the patent is invalid. The Patent Law stipulates: Article 42 The term of the invention patent right is 20 years, and the term of the utility model patent right and the design patent right is 10 years, both of which are counted from the date of filing. Article 43 The patentee shall pay the annual fee from the year when the patent right is granted. Article 44 In any of the following circumstances, the patent right shall be terminated before the expiration of the time limit: (1) Failing to pay the annual fee as required; (2) The patentee waives his patent right in writing. Where the patent right is terminated before the expiration of the time limit, it shall be registered and announced by the patent administration department of the State Council.