I'm trying to build a bottom bar with center button like this:

but I can't show the bottom sheet as expected.

First try: showModalBottomSheet -> overlays bottomnavbar, tried adding margin with transparent background and no opacity but I can't tap navigation bar anymore to close it

Second try: showBottomSheet -> error The following assertion was thrown while handling a gesture:No Scaffold widget found. So I tried using scaffoldKey but I couldn't close the sheet pressing outside or any other BottomNavigationBarItem, only scrolling down.

How can I build the same dialog and behavior as PayPal?