diff --git a/src/main/java/pink/zak/minestom/towerdefence/ui/spawner/TroopSpawnerUI.java b/src/main/java/pink/zak/minestom/towerdefence/ui/spawner/TroopSpawnerUI.java
index 525620b..ebee31c 100644
--- a/src/main/java/pink/zak/minestom/towerdefence/ui/spawner/TroopSpawnerUI.java
+++ b/src/main/java/pink/zak/minestom/towerdefence/ui/spawner/TroopSpawnerUI.java
@@ -31,6 +31,7 @@
 import pink.zak.minestom.towerdefence.queue.QueueFailureReason;
 import pink.zak.minestom.towerdefence.storage.MobStorage;
 import pink.zak.minestom.towerdefence.ui.ConfirmationUI;
+import pink.zak.minestom.towerdefence.upgrade.MobUpgradeFailureReason;
 import pink.zak.minestom.towerdefence.upgrade.UpgradeHandler;
 import pink.zak.minestom.towerdefence.utils.Result;
 
@@ -182,7 +183,14 @@ private void attemptToUnlockMob(@NotNull Player player, @NotNull UpgradeHandler
         }
 
         player.openInventory(new ConfirmationUI(player, Component.text("This action will cost you $" + cost + ".", NamedTextColor.RED), result -> {
-            if (result) upgradeHandler.unlock(mob);
+            if (result) {
+                if (upgradeHandler.unlock(mob) instanceof Result.Failure<MobUpgradeFailureReason> failure) {
+                    player.sendMessage(switch (failure.reason()) { // todo: better feedback
+                        case ALREADY_AT_LEVEL -> "You have already unlocked this mob.";
+                        case CANNOT_AFFORD -> "You can not afford to unlock this mob.";
+                    });
+                }
+            }
             player.openInventory(this);
         }, false));
     }
diff --git a/src/main/java/pink/zak/minestom/towerdefence/ui/spawner/TroopUpgradeUI.java b/src/main/java/pink/zak/minestom/towerdefence/ui/spawner/TroopUpgradeUI.java
index f931541..c4bb353 100644
--- a/src/main/java/pink/zak/minestom/towerdefence/ui/spawner/TroopUpgradeUI.java
+++ b/src/main/java/pink/zak/minestom/towerdefence/ui/spawner/TroopUpgradeUI.java
@@ -12,7 +12,9 @@
 import pink.zak.minestom.towerdefence.model.mob.config.EnemyMob;
 import pink.zak.minestom.towerdefence.model.mob.config.EnemyMobLevel;
 import pink.zak.minestom.towerdefence.model.user.GameUser;
+import pink.zak.minestom.towerdefence.upgrade.MobUpgradeFailureReason;
 import pink.zak.minestom.towerdefence.upgrade.UpgradeHandler;
+import pink.zak.minestom.towerdefence.utils.Result;
 
 public final class TroopUpgradeUI extends Inventory {
 
@@ -85,7 +87,12 @@ public void onClick(int slot) {
         EnemyMobLevel level = this.mob.getLevel(clickedLevel);
         if (level == null) return;
 
-        this.gameUser.getUpgradeHandler().upgrade(this.mob, level);
+        if (this.gameUser.getUpgradeHandler().upgrade(this.mob, level) instanceof Result.Failure<MobUpgradeFailureReason> failure) {
+            this.gameUser.getPlayer().sendMessage(switch (failure.reason()) {
+                case ALREADY_AT_LEVEL -> "You already have this level!";
+                case CANNOT_AFFORD -> "You cannot afford this upgrade!";
+            });
+        }
         this.refresh();
     }
 
diff --git a/src/main/java/pink/zak/minestom/towerdefence/upgrade/MobUpgradeFailureReason.java b/src/main/java/pink/zak/minestom/towerdefence/upgrade/MobUpgradeFailureReason.java
new file mode 100644
index 0000000..cc97903
--- /dev/null
+++ b/src/main/java/pink/zak/minestom/towerdefence/upgrade/MobUpgradeFailureReason.java
@@ -0,0 +1,8 @@
+package pink.zak.minestom.towerdefence.upgrade;
+
+public enum MobUpgradeFailureReason {
+
+    ALREADY_AT_LEVEL,
+    CANNOT_AFFORD
+
+}
diff --git a/src/main/java/pink/zak/minestom/towerdefence/upgrade/UpgradeHandler.java b/src/main/java/pink/zak/minestom/towerdefence/upgrade/UpgradeHandler.java
index 9d87020..9590ed8 100644
--- a/src/main/java/pink/zak/minestom/towerdefence/upgrade/UpgradeHandler.java
+++ b/src/main/java/pink/zak/minestom/towerdefence/upgrade/UpgradeHandler.java
@@ -10,6 +10,7 @@
 import pink.zak.minestom.towerdefence.model.mob.config.EnemyMob;
 import pink.zak.minestom.towerdefence.model.mob.config.EnemyMobLevel;
 import pink.zak.minestom.towerdefence.model.user.GameUser;
+import pink.zak.minestom.towerdefence.utils.Result;
 
 public final class UpgradeHandler {
 
@@ -36,27 +37,28 @@ public boolean has(@NotNull EnemyMob mob, @NotNull EnemyMobLevel level) {
         return Optional.ofNullable(this.mobs.get(mob));
     }
 
-    public boolean unlock(@NotNull EnemyMob mob) {
+    public @NotNull Result<MobUpgradeFailureReason> unlock(@NotNull EnemyMob mob) {
+        //noinspection DataFlowIssue there will always be a level 1
         return this.upgrade(mob, mob.getLevel(1));
     }
 
-    public boolean upgrade(@NotNull EnemyMob mob, @NotNull EnemyMobLevel level) {
+    public @NotNull Result<MobUpgradeFailureReason> upgrade(@NotNull EnemyMob mob, @NotNull EnemyMobLevel level) {
         return this.upgrade(mob, level, false);
     }
 
-    public boolean upgrade(@NotNull EnemyMob mob, @NotNull EnemyMobLevel level, boolean free) {
+    public @NotNull Result<MobUpgradeFailureReason> upgrade(@NotNull EnemyMob mob, @NotNull EnemyMobLevel level, boolean free) {
         // get current level
         EnemyMobLevel currentLevel = this.getLevel(mob).orElse(null);
 
         // check if the mob is already at the level
-        if (currentLevel != null && currentLevel.compareTo(level) >= 0) return false;
+        if (currentLevel != null && currentLevel.compareTo(level) >= 0) return Result.failure(MobUpgradeFailureReason.ALREADY_AT_LEVEL);
 
         if (!free) {
             // calculate cost of upgrade
             int cost = this.getCost(mob, level);
 
             // check if user can afford upgrade
-            if (this.user.getCoins() < cost) return false;
+            if (this.user.getCoins() < cost) return Result.failure(MobUpgradeFailureReason.CANNOT_AFFORD);
 
             // charge user for upgrade
             this.user.updateCoins(balance -> balance - cost);
@@ -72,7 +74,7 @@ public boolean upgrade(@NotNull EnemyMob mob, @NotNull EnemyMobLevel level, bool
                 level
         ));
 
-        return true;
+        return Result.success();
     }
 
     public int getCost(@NotNull EnemyMob mob, @NotNull EnemyMobLevel level) {