I tried to use SSL with Android 4.0. I have a .pem files (cert, chain, fullchain and key) and I read tutorials explaining how do to it, but the file extensions are different (I do not even know the difference between them, I can not follow a .crt tutorial if I have other files).
I believe it is not necessary to post code because all are similar, I want old versions of Android TRUST in my certificate, the newer versions open my site normally, but older show no connection available.
https://i.stack.imgur.com/cfSYj.png
In navigators at top my website have a green certified HTTPS Let's Encrypty Authority X3.
I own the Portecle download and skills with leading programming languages, responsive sites, upload with webviews and etc.