Changing the ' Only authenticated users can join meetings' setting

[shergar]

I use Calendly which enables participants to select their own meeting time etc and Zoom is the meeting platform configured within Calendly, so that the participant is sent a link for the actual meeting. However when they then try to join the meeting, they are being presented with a message that says “sign in to join this meeting, the host requires authentication on the commercial zoom platform to join this meeting. Please sign in with a commercial zoom account to join”

How do I change this so they don't have to have a zoom account too sign in to the meeting?