When I am inserting my full adder as a black box, I am getting the error as sum pin disconnected. can you please solve my query. The qll file is in above drive link.
the problem is hidden inside your full adder. You must bring your pins (input/output) at the bounding box edge.
In your full adder, the input pins are included in the bounding box making it not possible a direct connecting within the same layer.
Try using the attached one. Remember to replace all the black boxes within the CSA with the new one.