Hi Joe,
It seems to vary as to what users can and cannot join. I sent each user that had issues the invite link from the participants tab whilst the webinar was taking place and they said they could not connect and some even mentioned they needed to create accounts.
I asked them to try on both their laptop and phones through the browser as well and they still experienced issues.
The clients that registered using the registration tab built into the webinar also had issues with the "Join the Event" link.
I tried using my personal email address and it allowed me to initialize the session and gain access. I am not sure as to why it worked for me and not for the others.
Is there a workaround to ensure this doesn't happen again?