On the pictures, the hinge between the deck and tailgate is full of dirt/manure. That might prevent the gate from closing. Try cleaning everything first.

Another possibility is that the tailgate itself has warped, preventing it from closing properly.

A last possibility is the latches; either an alignment problem or a hardware malfunction.

"If the only tool you have is a hammer, every problem starts looking like a nail."

You can exchange "spud bar" for hammer if you like. Now there are phases in problem-solving when it is appropriate to use brute force. But problem analysis usually isn't one of them.

Things to try;

• Is the latch mechanism loose → fasten the bolts that hold it.
• Take of the ring or hook or whatever that is on the ends of the sides of the truck (or a piece of metal with the same thickness) and try engaging the latches on both sides with that. If both work, it is probably an alignment issue. If one side still won't engage, chances are it is broken and need replacement.

This is one of the relatively few things on a modern car that you can probably easily work on yourself, I think, before spending money on a mechanic.

It wouldn't surprise me if you can remove a plate covering the inside of the tailgate after removing some screws, exposing the mechanism.