[Edit] The bug is already fixed! Thank to the awesome admins of the server!! :d

Recently I saw chestshops on someone's plot and I was trying to sell them items, Nonetheless, an error saying "the flag 'use' is not set" was reported.

I searched on the internet and it seems like the following setting is the cause of the problem. By doing "/plot info" on any claimed plot, it's obvious that players are allowed to interact with the plot while holding item with ID = 323, or the block clicked on has ID = 68. The signs mounted on the side of a block, which has its ID = 68, is allowed to be interacted with players; however the blocked mounted on the top of a block with its ID = 63 isn't. The chestshops I tried to interact with have their signs mount on top of the chests, thus the permission denied error was thrown. (Please see the attached image below.)

Since we're not allowed to change the flags, I guess I can only ask the admins for help. Sorry for bothering.