Translation of the video description (by me):

[I] was at the wonderful obstacle course of “Construction World” in Herschweiler-Pettersheim. [It] was a wonderful day of driving, and the dumper worked marvelously. I only have to adjust the width slightly, so that it closes reliably again even when dirtied.

Homepage of Construction World:
https://www.construction-world.de/anfahrt/

[For] Who wants to buy it: [The dumper file for 3D printing]
https://cults3d.com/en/3d-model/game/tailgate-for-bruder-volvo-dumper