Add separate error message for invalid names

src/main/java/com/Acrobot/ChestShop/Configuration/Messages.java

@@ -89,6 +89,7 @@ public class Messages {
     public static Message PLAYER_NOT_FOUND;
     public static Message NO_PERMISSION;
     public static Message INCORRECT_ITEM_ID;
+    public static Message INVALID_CLIENT_NAME;
     public static Message NOT_ENOUGH_PROTECTIONS;
 
     public static Message CANNOT_CREATE_SHOP_HERE;

src/main/java/com/Acrobot/ChestShop/Events/PreTransactionEvent.java

@@ -247,6 +247,7 @@ public class PreTransactionEvent extends Event implements Cancellable {
         NOT_ENOUGH_STOCK_IN_INVENTORY,
 
         INVALID_SHOP,
+        INVALID_CLIENT_NAME,
 
         SPAM_CLICKING_PROTECTION,
         CREATIVE_MODE_PROTECTION,

src/main/java/com/Acrobot/ChestShop/Listeners/PreTransaction/ErrorMessageSender.java

@@ -113,6 +113,9 @@ public class ErrorMessageSender implements Listener {
             case INVALID_SHOP:
                 message = Messages.INVALID_SHOP_DETECTED;
                 break;
+            case INVALID_CLIENT_NAME:
+                message = Messages.INVALID_CLIENT_NAME;
+                break;
             case CREATIVE_MODE_PROTECTION:
                 message = Messages.TRADE_DENIED_CREATIVE_MODE;
                 break;

src/main/java/com/Acrobot/ChestShop/Listeners/PreTransaction/InvalidNameIgnorer.java

@@ -20,7 +20,7 @@ public class InvalidNameIgnorer implements Listener {
 
         String name = event.getClient().getName();
         if (ChestShopSign.isAdminShop(name) || !USERNAME_PATTERN.matcher(name).matches()) {
-            event.setCancelled(PreTransactionEvent.TransactionOutcome.CLIENT_DOES_NOT_HAVE_PERMISSION);
+            event.setCancelled(PreTransactionEvent.TransactionOutcome.INVALID_CLIENT_NAME);
         }
     }
 }

src/main/resources/languages/lang.en.yml

@@ -75,6 +75,7 @@ RESTRICTED_SIGN_CREATED: "Sign successfully created!"
 PLAYER_NOT_FOUND: "Player not found!"
 NO_PERMISSION: "You don't have permissions to do that!"
 INCORRECT_ITEM_ID: "You have specified an invalid item id!"
+INVALID_CLIENT_NAME: "Your username is not a valid Minecraft username!"
 NOT_ENOUGH_PROTECTIONS: "Could not create a protection!"
 
 CANNOT_CREATE_SHOP_HERE: "You can't create shop here!"