For Nginx-powered web server, I did this to make my site trusted:
cd /etc/letsencrypt/live/example/
cat cert.pem fullchain.pem > bundle.pem
Then I did this in my Nginx config file:
ssl on;
ssl_certificate /etc/letsencrypt/live/example/bundle.pem;
ssl_certificate_key /etc/letsencrypt/live/example/privkey.pem;