Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. https://crt.sh/?q=example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
My domain is: bglaw2.dscloud.biz
I ran this command: Tried to reach the above using Chrome and Firefox but cannot?
It produced this output: Cert. is expired. You cannot open the site.
My web server is (include version): Synology DS1520+
The operating system my web server runs on is (include version): Synology
My hosting provider, if applicable, is: Synology NAS
I can login to a root shell on my machine (yes or no, or I don't know): On my Dell Window 10 Pro I can open its Power Shell. Cannot open anything on the Synology NAS since I cannot reach it by browsers (Chrome or Firefox) because the Let's Encrypt Cert. did not renew. Need to renew that certificate? But how?
I'm using a control panel to manage my site (no, or provide the name and version of the control panel): The control panel is on the Synology NAS. Can't open as stated above.
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot): Do not know what this is asking of me?
The problem is your server is using a self-signed Synology cert instead. I'm not sure how to configure Synology devices. You can see the cert your server is using with a site like this SSL Checker
And, maybe this other thread will help with your Synology
I got it while on the Synology NAS (using Chrome or Firefox to access it). Those browsers will not connect now since the Cert. did not auto renew as it is supposed to. I think if I connect a laptop directly to the Synology NAS it will let me in (even using Chrome or Foxfire). Then I can go through the process of asking Let's Encrypt for a new Cert. I understand it will only tolerate just so many requests for a new Cert. (under any given email), and then perhaps you have to use some other email. I cannot recall the instructions about that. Anyway. I'll give it a try using the direct connect method referenced above (until now, I've just been opening a browser on one of our internal network connected Windows desktops and trying to go to bglaw2.dscloud.biz, which means it goes out to the internet and comes back - I think, but with direct connect, I might be able to use the Synology's local IP address 192. ... etc. to reach it. Will see.)
I hope I am directing this "Reply" to all who had a contribution to helping me solve my Let's Encrypt Cert. Renewal problem above. Each contribution was correct and each helped me along the way. Most notable perhaps was the note letting me know that sure enough my Cert. has been renewed. I am using 2 Synology NAS. One is used as a Reverse Proxy Server (bglaw.dscloud.biz), and that server pushes any request for bglaw2.dscloud.biz to that other NAS. The server references the other server and its Cert. Ports 80 and 443 are open to bglaw. Bglaw then passes anything asking for bglaw2 over to bglaw2. For some reason when renewal happened it happened on bglaw2 NAS, but not on bglaw NAS. So I exported the renewed Cert. from bglaw 2 NAS and picked it up on bglaw NAS and now I can access either NAS by https with no problem. Thanks to all of you who took time to contribute. Lots of great information delivered almost instantly. This is about the best "Community" of well versed pros I've used in a very long time. Hope I can contribute myself somewhere along the line in the future, but I have to confess that's not likely give my skill level. Maybe I'll learn. Thanks!