You should apply for a patent before the product is made public and put into use, otherwise the patent may become existing technology due to prior sales, and will eventually be invalid or lost due to the defense of existing technology. According to the patent attorney, when the patentee asks about the prospect of the case with products and patent certificates suspected of infringement, the first question they need to know is: Has the patent application been exhibited and sold to the outside world at present? This problem is especially fatal to design patents. Inventions and utility model patents generally involve internal structure, which is difficult to prove. And design patents often only need to take photos of web pages (such as Taobao's sales records).