Participants do not see chat icon / chat messages

I had already had 2 webinars where the participants do not see the chat icon nor do they see that I have sent anything in it. I - as host - can see the chat icon and can send in messages. I have made sure that it says 'to everyone' and on the Zoom web portal I have also made sure that everything concerning the chat is on.
What else could be the problem here?