Help❓ Bad serial number given in Setup

Hi guys :b
I bought a new key
And i changed it with the DarkyKeyChanger
And if join a server the error appears "Bad serial Number given up in Setup"
I tried some fixes but i think i make everytime a mistake.
Please help!!

The key you bought is more then likey Invaild or after you changed your key you downloaded and ran a keystealer