Sign won't change onSignEvent

Code:

Code:java

    @EventHandler
    public void onSignChange(SignChangeEvent e) {
        Player p = e.getPlayer();
        if (e.getLine(0).contains("[buydiamond]")) {
                e.setLine(0, "§b[Diamond]");
                p.sendMessage(ChatColor.GREEN + "Diamond sign created!");
          }
    }

Whenever I type [buydiamond] on a sign, it doesn't change. Could you help me?
Thank you

 

Code:java

    @EventHandler
    public void onSignChange(SignChangeEvent e) {
        Player p = e.getPlayer();
 
        if (e.getLine(0).equalsIgnoreCase("[buydiamond]")) {
                e.setLine(0, "§b[Diamond]");
                p.sendMessage(ChatColor.GREEN + "Diamond sign created!");
          }
    }

 

Make sure the class implements Listener and you register the event.