For your on-premise instance to know about updates or to download updates, it must be able to communicate with our version server by downloading a manifest file. If your server is unable to download the manifest file, then your instance won't be able to use the automatic updater and it also won't know if/when new updates are available. The possible reasons for this are usually one of two things:
Your server is blocking outbound connections
For example, servers on intranets might not even have access to the internet. Or you might have a firewall blocking requests. Finally, some RHEL/CentOS users might need to disable or tweak SELinux settings to allow PHP to make http requests.
Your server has old SSL root certificates
Deskpro's version manifest file is served over HTTPS. Every server has a collection of root "trusted" SSL certificates that it uses to verify connections. From time to time, these trusted root certificates are updated. If your server has an old collection of root certificates (i.e. you do not have it configured to auto-update certificates from a trusted vendor), then the HTTPS connection will fail because your server is unable to verify our certificate.
You can manually update your SSL trusted root certificate store by following this guide.
You can try to run the 'status' command from the command-line. This will attempt to check your version against the manifest, and if a problem occurs, it will show you an error message:
/path/to/php bin/console dp:update:status
You can also verify that normal networking works by trying to fetch the manifest manually from the command-line by using a tool like wget or cURL. For example:
If this fails, then it's proof that your server can't reach the manifest file at all (e.g. a firewall). Note that if this does work, it still does not exclude a server issue because it's possible specific software is protected with a firewall, SELinux, etc.