Missing Code Signing Certificate in Profile Manager

Hi everyone,

Firstly, I'm not a professional and managing a server isn't in my skill set. I have an old Mac mini running the Mavericks server to dabble with.

Recently, the code-signing certificate (I assume self-signed) disappeared from Profile Manager for the option to "Sign configuration profiles" – no idea why, and I'm struggling to get it back, it just doesn't appear in the drop down.

Under "Certificates" in Server.app, and within Keychain Access; it's still in the system and can be seen, where there are two of them.
I've tried renewing both of these through Server.app to see if that would be a quick fix, but nothing.

Could someone advise me on how to create a new verified code signing certificate for use with profile manager?

Kind regards,

Jamie