I got your points On Cloudflare, I only enabled SSL -> FULL ( in Crypto tab), on my DirectAdmin control panel, I enabled Letsencrypt ssl by generate cert key for it. Just that and I could use https for my site. I read some guys on my site said using Certbot to renew Letsencrypt SSL certificate or running this command ./letsencrypt-auto renew but I am not sure about them, if using Certbot can help me to renew Letsencrypt then I would give it a try. Thanks