They took the old screen out of a screen door. But forgot how is was?
The spline channel rounds around the door. But in the middle there is also a spline channel, running across the middle of the door, At the bottom of the door is another spline channel
Do you spline the entire door on its outer edge around the door? Or is it screened in two sections? See pictures

It should be screened with one long piece top to bottom. Those cross spines are not used. Have you ever done a replacement before, there are a few tricks to make the screen really tight.

I did a few windows. But never a screen door.

Put the door on a flat work table with a 2x4 under each end 4" side down. Clamp the door in the middle with two C clamps on each side rail. Tighten the clamps so the down is slightly defected into a slight arc. Once you get the screen in and the rubber spine firmly inserted you the release the clamps. Your screen with be tight as a drum.

Okay great. Maybe that crossbar is just there for rigidity purpose