Zoom Events: Ticket invitations not being sent

Hi everyone, 

We're holding a Zoom conference in September on Zoom events.  We're offering both a paid for ticket option and a free ticket for our stakeholders.  I've created the free ticket and set it to only be available for people we invite.  I've added a couple of people to the guest list for the free ticket and that's been fine, but now I keep getting a red "Server error" alert come up at the top of the screen when I try to add anyone new and then the invites aren't sent, the guest list just reverts back to the original two guests I'd added. 

Any ideas as to why this is happening?  Would really appreciate some guidance!