I have added someone to a teams meeting chat but they can't see it, I then tried to remove them from the chat and re add them but they still can't see it?

Question

I set up a meeting, and want to utilise the chat. After the meeting I added a user to the meeting invite thinking this would grant them access to the chat but it didn't (they are however showing on the list of people). I removed them and re added them but they still cannot see the chat? Please help.