This is because in the list table, you did not name the property you want to be changed so the function sees it as an array and doesn’t know what property to change
local list = { -- what it looks like
[1] = Vector3.new(25,25,25)
}
local PropertyName = "Size"
local list = { -- what it should be
[PropertyName] = Vector3.new(25,25,25)
}