Why is the Let's Ecrypt certificate not trusted in some browsers?

Question

Google

Hello, I use BillManager on the server, but I think this is not related to my problem.
I recently created a Let's Encrypt certificate, uploaded all the certificate data to ihttpd (server on CentOS), the certificate worked in Chrome, wrote that the site was verified. The next day I look .. The site is not confirmed (BUT EVERYTHING WORKS YESTERDAY), the certificate was created just yesterday. I decided to check, I went to Samsung Browser (preinstalled) - the same mistake. I went to Yandex.Browser - the site is confirmed, green color .. What's the problem? Help!

Answer 1

The reason is not the correct configuration of the virtual host. You need to register intermediate certificates. Simply put, in the field with the certificate, you need to write not cert.pem, but fullchain.pem
Here, it seems like a suitable description of how it is configured.
https://habrahabr.ru/post/318952/

Answer 2

just in case https://zerossl.com/free-ssl
I use, there are no problems