Confirmation link not working

With a meeting I organized and hosted, some of my meeting participants could not access the meeting.  This is what one of them said:

I definitely had issues today. I was registered for the meeting prior to today and even got the email with the meeting link this morning. However when I went to join the meeting it redirected me to register again. I tried several times to join from my computer and phone but it still requested me to register for the meeting again.