How to build a bridge over canyon

Hi im trying Forever now on building a bridge over a canyon . But units won’t get over it? They try to walk down the Canyon through the bridge like its invisible or something. The red spline from the bridge is also drawn to the bottom of the canyon on the side of the canyon walls. Can someone please help me with some pictures for guidance . My thanks so great and will help me to go further with the awesome map.
Grtz Braindeath