when I try to do it, it just says "unknown command, type /help for help".

Can you give me an example?

first of all, i just downloaded the latest version on jenkins, and part of the issue is fixed. Now it says the correct usage of the sentence.
You probably know that in the command block, the term @p is for the nearest player, but when i try to use it , it says the correct way of using the command. Maybe simpleclans just doesn't support de usage of @p, @r, etc.?

PS.: i already tried using "sudo"

Can you give me an example of the command you are using?

i am using : "sudo -u flgmjr clan place @p H4GRed"
oh, I am an op at the server.

Its a bug in Spigot. I tested with Spigot 1.8.7 and it works fine. Its broken on Spigot 1.8.

Details of the bug here

thank you man! And i am bothering you with this because i tested a lot of plugins but your's is just the best one i found! Thank you again!