I’m not able to request a new certificate with my Synology DS218+. I’ve set my Synology back to the factory settings, but I forgot to export the certificates (because I thought my back up would take care of it, which it doesn’t did)
Now i’m requesting a new certificate for my domain and subdomains and there keeps popping up a error message…
What can I do to troubleshoot this? Nothing has changed with my ports in my router or anything like that. The situation is still exactly the same as it was when it was working…
Do you have a firewall that might be blocking connections from some addresses? Let's Encrypt validation now requires connections to succeed from multiple places on the Internet (which wasn't required in the past).
I think this is also good advice—Synology may have fixed a number of bugs or incompatibilities over time which your rollback could potentially have reintroduced (depending on how far back your version was downgraded).
If neither of these ideas helps, I think you'll need to look for a way to get more specific error logs from the Synology device so that we can understand why the certificate issuance isn't succeeding.