commands are not working in server (Aternos)

[boreal pagoda]

console:

fortress
[23:43:18] [Server thread/INFO]: Unknown or incomplete command, see below for error
[23:43:18] [Server thread/INFO]: fortress<--[HERE]
fort
[23:43:20] [Server thread/INFO]: Unknown or incomplete command, see below for error
[23:43:20] [Server thread/INFO]: fort<--[HERE]
for
[23:43:21] [Server thread/INFO]: Unknown or incomplete command, see below for error
[23:43:21] [Server thread/INFO]: for<--[HERE]

client side:

i want to enable border in aternos

[boreal pagoda]

i tried localhost server and i still can't use the command to enable the border