Why has the opportunity I've been invited to changed the status to closed?

The status helps everyone keep track of what's going on.

If the manager updates the status to 'closed' that usually means they have received sufficient interest and they wish to stop further interest coming through. This doesn't necessarily mean you're out of the game - they might contact you next!

Sometimes managers do get really busy, which makes reaching out to all of the fantastic people like you to let them know feedback impossible. 

Don't worry though, there will be lots more opportunities coming your way, so keep that profile up to date.

Good luck!