To start off with, you have to open lua/ll_plates/config/sh_misc.lua with your text editor of choice.
NOTE: In versions below 3.16.0, this is instead in conf_misc.lua
NOTE: In versions below 3.4.0, this is instead in sh_debugging.lua.
Once that's been done, go to
PLATE.Config.DoDebugPrints = false
and change it to
PLATE.Config.DoDebugPrints = true
Once you've done that, save and re-upload the file, then restart the server. This creates debug files in the root data folder of both the server and client.