If it is still under warranty, have the dealer fix it, or: Open drivers door and look at the latch position, then see if the passenger latch is in the same position. If not, try to flip it so that it is the same as the drivers side. If it just flops up and down, you have a latch that is ether internally gummed up, or internally damaged. You would then likely need a new replacement latch assembly. To access the door latch assy, the door panel will need to be removed. If you do not feel confident doing that level of repair, you should take it to a qualified mechanic.
The passenger door latch issue seems to be a common theme with 2013 Ford Fusions. I experienced the same issue today, and am riding around with my car door taped shut because the Ford delearship estimates that the cost to rfepair the door latch issue will be around $400.