If you are sending it with a trusted courier then just lock the key onto the shackle and let your friend break it off when he receives it. (He’ll be able to tell if it was tampered with or not.)
If not- send the box with one lock, have your friend attach another lock (while keeping the key to himself) and send the box back to you.
Now you can remove the lock you put on originally and send the box back with only the lock that he put on.