I used to be using Acuity scheduling but I migrated away from it specifically because it didn't allow for a scheduler to invite guests. Now I have three other schedulers besides Simplero available for my use, and they all allow the scheduler to invite a guest.

Most of my meetings involve 3 or 4 people. Without this option, my contacts just forward the invite to the rest of their team and I don't have the ability to track who is supposed to be attending.