When should the examination fee for invention patents be paid?

substantive examination fee: it can be paid at any time within three years after the application, and it is best to submit a request for substantive examination at the same time, without waiting for the notice of preliminary examination. In addition, whether to pay the substantive examination fee or not will start the preliminary examination procedure. Just don't pay the substantive examination fee will not start the substantive examination procedure. You can now wait for the notice of passing the preliminary examination and the notice of publication of the invention patent.