I get an “Access Denied” error, so I guess it’s for admins only.
It’s strange, because today I was just notified by the system:
Member
This badge is granted when you reach trust level 2. Thanks for participating over a period of weeks to truly join our community. You can now send invitations from your user page or individual topics, create group personal messages, and have more likes per day.
So, apparently the forum software should have some invitation functionality, maybe it’s just disabled.
I’ve tried looking up the feature in Discord documentation, but it’s not crystal clear:
https://support.discord.com/hc/en-us/articles/208866998-Invites-101
So, possibly it’s an admins only feature, or one limited to community members (or public forums).
Yesterday I changed the requirements for moving to Trust Level 2 and then I manually moved you to that level because of this 
Discourse is powerful but a bit complex to use, I will dig some more into this