I installed InvoiceNinja some time ago on a shared hosting, using the ZIP method. I installed v5.5.124-C118.
The docs said it would update itself, but it seems that this isn’t the case for me, as my instance is still at v5.5 but the latest release is at v5.10.
I created the cron command, but its output is always:
If you have installed the application using the precompiled .zip file, then the internal self updater should perform all the necessary tasks to bring your app up to the latest version.
It appears this may be a bug at the moment. It’s been reported several times on GitHub that users aren’t being notified when updates are available. I believe the developers are looking into the situation. Edit: This appears to be fixed. I can confirm it shows up again in version 5.10.20 for the most recent update to v.5.10.21.
Given how old your installation is, you’ll need to upgrade via CLI. As @hillel said, you need to also upgrade PHP. I’m guessing you’re also on an older version of the OS. If you’ve updated Ubuntu (and other) base OS, it would have updated PHP automatically.
If you’re unfamiliar with that big of an upgrade, you might be better off copying the database and standing up a brand new instance. If not something you do regularly, there are many moving parts that can pose problems.