Hi, everyone, who faced problem with making SD more safe with letsencrypt :)

At 18365 attempt i've made it with my system, however, it would be helpful for other.

So:

1. Obtain your .pem file (already with information of your domain name encrypted inside) and split it into .crt, .key, .csr and ca-crt.crt files

2. Copy https://letsencrypt.org/certs/trustid-x3-root.pem.txt and paste it inside the trustid-x3-root.pemfile you should create to

3. Download XCA https://sourceforge.net/projects/xca/ software and install it

4. Import all the certs you've created to XCA 

5. In a Certificates tab press Export button and choose PKCS#7 chain (*.p7b) option then press OK (it should be exported to the same dir where all other certs are placing)

6. add that <yourdomain>.p7b into the system within the Admin panel - Import SSL Certificate.

7. System would ask you to add .key file. Choose it  from 1 paragraph.

8. Now most exciting - Press add and wait for miracle (as it was for me).

9. Last step - you should restart your server and i hope you to enjoy that SD accepted all that.