Does anyone know how to add another Mullion on the window?

[jgarciacorpus69]

Been trying for a while how to add a Mullion but won't let me. I clicked on the middle and nothing happens. 

If anyone can show me how it could be done so I could move on to the issue I have with the roofing 

Thank you 

[ToanDN]

TAB on the curtain grid and Add Segment and click where you want the mullion is.

[jgarciacorpus69]

I clicked on the grid to add the segment and only made a line, I clicked on that line but the Mullion did not continue, did I do something wrong ? 

[ToanDN]

That is a good 1st step.  Now click the Mullion tool to add a Mullion to that segment.