Why are self-signed certificates not trusted? Because the operating system doesn't trust your certificate chain, now commercial certificates are issued by CA only after being trusted by major browsers and operating systems. If you want to trust your self-signed certificate, you need to add a trusted root certificate manually. For details, please consult 12306. When purchasing tickets online, you need to manually add their root certificates. Unless your website is necessary for customers, you should choose a business certificate, which is safer.