diff --git a/app/Livewire/Forms/Studio/Manage/OrderForm.php b/app/Livewire/Forms/Studio/Manage/OrderForm.php
index 1aff99d..70d13dc 100644
--- a/app/Livewire/Forms/Studio/Manage/OrderForm.php
+++ b/app/Livewire/Forms/Studio/Manage/OrderForm.php
@@ -109,7 +109,7 @@ public function store(): array
         $discount = $voucherDiscount + $manualDiscount;
 
         // Calculate total (subtotal - manual discount - voucher discount)
-        $total = $afterManual - $voucherDiscount;
+        $total = max(0, $afterManual - $voucherDiscount);
 
         $pointsEarned = (int) floor($total / 5000);
 
@@ -141,7 +141,7 @@ public function store(): array
                     // Deduct item stock from the outlet inventory
                     $result = $this->decreaseOutletStock($order->outlet, $item);
 
-                    if ($result && ! $result['status']) {
+                    if (! $result['status']) {
                         throw new \Exception($result['message']);
                     }
 
@@ -161,27 +161,35 @@ public function store(): array
 
                 // Deduct voucher quantity
                 if ($this->voucher_id) {
+                    if (! $member) {
+                        throw new \Exception('Data member tidak valid.');
+                    }
+
                     $userVoucher = DB::table('user_voucher')
                         ->where('user_id', $member->id)
                         ->where('voucher_id', $this->voucher_id)
                         ->lockForUpdate()
                         ->first();
 
-                    if ($userVoucher) {
-                        if (! $userVoucher->quantity) {
-                            return;
-                        } elseif ($userVoucher->quantity > 1) {
-                            DB::table('user_voucher')
-                                ->where('id', $userVoucher->id)
-                                ->update([
-                                    'quantity' => $userVoucher->quantity - 1,
-                                    'updated_at' => now(),
-                                ]);
-                        } else {
-                            DB::table('user_voucher')
-                                ->where('id', $userVoucher->id)
-                                ->delete();
-                        }
+                    if (! $userVoucher) {
+                        throw new \Exception('Member tidak memiliki voucher ini.');
+                    }
+
+                    if ($userVoucher->quantity < 1) {
+                        throw new \Exception('Voucher sudah habis terpakai.');
+                    }
+
+                    if ($userVoucher->quantity > 1) {
+                        DB::table('user_voucher')
+                            ->where('id', $userVoucher->id)
+                            ->update([
+                                'quantity' => $userVoucher->quantity - 1,
+                                'updated_at' => now(),
+                            ]);
+                    } else {
+                        DB::table('user_voucher')
+                            ->where('id', $userVoucher->id)
+                            ->delete();
                     }
                 }
 
diff --git a/app/Traits/Order/WithCalculateTotal.php b/app/Traits/Order/WithCalculateTotal.php
index abc967e..35fbe44 100644
--- a/app/Traits/Order/WithCalculateTotal.php
+++ b/app/Traits/Order/WithCalculateTotal.php
@@ -11,6 +11,8 @@ public function getSubTotal(): int
 
     public function getTotal(): int
     {
-        return $this->items->sum(fn ($item) => $item->unit_price * $item->quantity - parseRupiahToInt($this->form->discount) - $this->voucherDiscount);
+        $subtotal = $this->items->sum(fn ($item) => $item->unit_price * $item->quantity);
+
+        return max(0, $subtotal - parseRupiahToInt($this->form->discount) - $this->voucherDiscount);
     }
 }
diff --git a/app/Traits/Order/WithUpdateStock.php b/app/Traits/Order/WithUpdateStock.php
index 2a4fa4a..c2a2f16 100644
--- a/app/Traits/Order/WithUpdateStock.php
+++ b/app/Traits/Order/WithUpdateStock.php
@@ -27,7 +27,11 @@ public function increaseOutletStock($outlet, $item): void
                 return;
         }
 
-        $existing = $outlet->{$relation}()->withPivot('stock')->where("{$relation}.id", $item->orderable_id)->first();
+        $existing = $outlet->{$relation}()
+            ->withPivot('stock')
+            ->where("{$relation}.id", $item->orderable_id)
+            ->lockForUpdate()
+            ->first();
 
         if ($existing) {
             $currentStock = $existing->pivot->stock ?? 0;
@@ -112,5 +116,7 @@ public function decreaseOutletStock($outlet, $item)
                 'purchase_id' => $item->purchase_id ?? null,
             ]
         );
+
+        return ['status' => true];
     }
 }