Help, how do I get item down from ledge. Grimstone Building Rooftop

https://reddit.com/link/1s9bun0/video/ly5h2bpqnisg1/player

How can I get the gunpowder down from that ledge? This is my second playthrough. An item has appeared on the ledge in my previous playthrough (shot gun ammo); however, I ignored it, assuming it was there due to some error. Now during my second playthrough, there is gun powder in the same location. Has anyone else encountered this? Were you able to get the item down, if so . . . HOW? Please help.

Thank you for your time.