When you try and access a meeting you either did not attend or you are not in the relationship in which that meeting is part of, you need to request access.
The process is simple, you request access, the meeting owner gets an email, and once approved you get an email.
The meeting owner will get an email like this, which gives them the option to either allow access to a single meeting or to add you to the meeting's relationship so you have access to all future related meetings, without having to request access.
Once your request has been approved, you will get an email. If you don't get an email it simply means that the meeting owner has not yet approved access.