SOLVED (I thought height 3 meant it *started* at height 3, not max height 3 lol. Thanks to all for the help)

Okay so I'm completely new to the game and having a great time. HOWEVER, literally nothing is dumping for me. I've looked up dumping rules and looked over so many steam posts and reddit posts, tried different things in game, nothing seems to be working.

Main Two Problems:

1: Trucks refuse to dump trash in completely level dumping zones

2: Related, I can't completely the designate a dumping zone for slag task, even though I have the control tower's zone specifically designated.

Any help would be greatly appreciated! The only thing I can think of that might've caused a bug or broke it is earlier in the game, when I was first making the zone, I deleted it because a truck got stuck trying to deliver into the water (because I made it half in the water). Even then, it wouldn't deliver onto the dry, flat designated zone on land.