what is this broken metal rod visible in rear wheel well?

What is this broken metal rod and does it matter? didnt know it was broken till i was adding air in my tires during daylight. It seems to connect the frame near the rear spring shackles to the bed side body panel? The other side is intact. this must be the rustiest part of the whole truck.

it holds the side of the box in place,, should be connected on both ends, one to the frame, the other to the box flange,,

Yep, it's just a brace to keep the body panel from moving.