Pin a Meeting Point to a floor
Where the Area of Interest you picked has floors, you can say which one you mean, and the Meeting Point is then described with it: Beer Garden — Floor 2 rather than just Beer Garden. Without a floor it is the Area as a whole, which is the right answer for a single-storey place and an ambiguous one for a building.
Floors exist only where the person who made the Map drew them, so the option is not offered on an Area that has none — that is the Map, not your phone. The creator’s side of it is add floors to an Area.
Pinning a floor changes what the Meeting Point is called, not who can see it. Everybody in the Group still gets the same notification and sees the same flag on the Map; what they gain is the one detail that stops four people standing on four different levels of the same building.