Making an added function module (to a function group) visible in SE80

After creating an (additional) function module within a function group, it wasn't visible within SE80 after it was transported to another BW system.
When displaying the function group, via transaction SE80 --> Function Group, the newly created function module WAS NOT visible, even though the import/transport ended without errors.
The trick, to make all function modules visible within the function group, is to update the navigation index as shown in the screen-grab below: