Translation:Next time I am going to place it on your door.
Auxbuss, I am going to use your term "USian English" from now on. I love it! Anyway, as a USian person, I also translated the phrase into "AT your door," which was my first inclination, seemed natural to me, and was accepted by DL. It is general enough to mean on your front step (maybe in a box or else weighted under a rock), or wedged between the door and the door jamb, or slipped under your door, or between the screen/storm door and permanent door. If the item in question is a five foot tall chicken made in Mexico out of brightly colored scrap metal, then I would just leave in front of your door, ring your doorbell, and run away. Thanks for USian.
"... place it at your door" was not accepted. "En" can also mean "at", can't it? The only thing you might place on a door is a note. If it were an article, you would be more likely to place it "at your door", or "inside your door" or "on your doorstep". Thanks to the Duolingo crew for all the fantastic help.