Where do we go to pay whatever we want to get in?

You can pay ONLY WHAT YOU WANT for the museum at any entrance. If yoy want to see the attraction at the Planitarium, it is a set price.

There's an entrance on the 82nd St side that is less busy than the main entrance. Go down the elevator and go to the ticket counter in the corner.

You want in and theres a lineup for the cashiers/ticket desks. Otherwise if you buy the tickets online for 23$ you can walk right in and scan yoyr ticket no lineup!