How many days at the latest after the patent payment notice comes down?

It should be the fees you are told to pay in the authorization notice, and these fees should be paid within two months from the date of receiving the notice of granting the patent right and going through the registration formalities.

Patent fees include application fee, examination fee of invention substance, reexamination fee and change fee of recorded items, etc. The applicant needs to pay the corresponding fees for restoring the rights or extending the patent term. The parties may, within three years from the date of payment, request the refund of the overpaid, re-paid or wrongly paid patent fees. If it is really difficult for the applicant or the patentee to pay the patent fee, he may request a postponement. The patent time is annual, and an annual fee is required; If the payment is not made on time or insufficient, it is necessary to pay the late payment fee in time.