Webinar - adding an external presenter before the meeting

Hello thanks for the reply. I do understand the differences. I was hoping to promote the presenter before the meeting because it's not easy to promote someone in a meeting with over 500 people. You can do it but it takes time to find their names and promote them. This can cause a delay during the meeting and doesn't look professional. To be honest, I was able to do it once before around a month ago. I added them as optional presenter and their name appeared in the drop down list for presenters. For some reason, I can't do it now. I tested it with another company and their tenant was able to do it. So weird that I can't anymore.