I'm taking a class right now and I'm having a problem with creating a Rib. My rib feature appears to be missing the "flip material side" feature.

My part:

The process I used is as follows:

1)  Make a basic "L" Shaped frame in a sketch

2) Extrude out the part

3) Make a Reference Plane in the middle of the object.

4) Draw line for rib (The points are coincidental)

5) Fail to make Rib because flip option is missing. While this one technically works, my main none does not.

What it should look like