diff --git a/app/Http/Controllers/Admin/BasicSettings/PaymentConfigController.php b/app/Http/Controllers/Admin/BasicSettings/PaymentConfigController.php
index 080dab4..fd769e7 100644
--- a/app/Http/Controllers/Admin/BasicSettings/PaymentConfigController.php
+++ b/app/Http/Controllers/Admin/BasicSettings/PaymentConfigController.php
@@ -51,7 +51,7 @@ class PaymentConfigController extends AdminController
             'name' => 'required|string|max:255',
             'company_id' => 'nullable|exists:companies,id',
             'settings' => 'required|array',
-        ]);
+        ] + $this->ecpayInvoiceRules(), $this->ecpayInvoiceMessages());
 
         PaymentConfig::create([
             'name' => $request->name,
@@ -83,7 +83,7 @@ class PaymentConfigController extends AdminController
             'name' => 'required|string|max:255',
             'company_id' => 'nullable|exists:companies,id',
             'settings' => 'required|array',
-        ]);
+        ] + $this->ecpayInvoiceRules(), $this->ecpayInvoiceMessages());
 
         $paymentConfig->update([
             'name' => $request->name,
@@ -105,4 +105,30 @@ class PaymentConfigController extends AdminController
         return redirect()->route('admin.basic-settings.payment-configs.index')
             ->with('success', __('Payment Configuration deleted successfully.'));
     }
+
+    /**
+     * 綠界電子發票群組驗證規則：整組選填，但只要填了任一欄，
+     * store_id / hash_key / hash_iv / email 即全部必填（綠界開立發票需金鑰齊備，
+     * 且 email 為「電話／信箱擇一」的唯一來源，缺一即無法開立）。
+     * 依賴 ConvertEmptyStringsToNull middleware：空欄送出為 null，required_with 不會誤觸發。
+     */
+    private function ecpayInvoiceRules(): array
+    {
+        $g = 'settings.ecpay_invoice';
+        return [
+            "{$g}.store_id" => "nullable|string|max:20|required_with:{$g}.hash_key,{$g}.hash_iv,{$g}.email",
+            "{$g}.hash_key" => "nullable|string|max:64|required_with:{$g}.store_id,{$g}.hash_iv,{$g}.email",
+            "{$g}.hash_iv" => "nullable|string|max:64|required_with:{$g}.store_id,{$g}.hash_key,{$g}.email",
+            "{$g}.email" => "nullable|email|max:100|required_with:{$g}.store_id,{$g}.hash_key,{$g}.hash_iv",
+        ];
+    }
+
+    /** 綠界電子發票群組的驗證訊息（三語系）。 */
+    private function ecpayInvoiceMessages(): array
+    {
+        return [
+            'settings.ecpay_invoice.*.required_with' => __('ECPay e-invoice is optional, but once any field is filled, Store ID / Hash Key / Hash IV / Email are all required.'),
+            'settings.ecpay_invoice.email.email' => __('Please enter a valid ECPay e-invoice notification email.'),
+        ];
+    }
 }
diff --git a/lang/en.json b/lang/en.json
index 24fd147..af9f119 100644
--- a/lang/en.json
+++ b/lang/en.json
@@ -609,6 +609,7 @@
     "EASY_MERCHANT_ID": "EASY_MERCHANT_ID (EasyWallet)",
     "ECPay Invoice": "ECPay Invoice",
     "ECPay Invoice Settings Description": "ECPay Invoice Settings Description",
+    "ECPay e-invoice is optional, but once any field is filled, Store ID / Hash Key / Hash IV / Email are all required.": "ECPay e-invoice is optional, but once any field is filled, Store ID / Hash Key / Hash IV / Email are all required.",
     "ECPay has no such invoice; marked as pending re-issue": "ECPay has no such invoice; marked as pending re-issue",
     "ECPay query failed": "ECPay query failed",
     "ESUN": "ESUN",
@@ -1404,6 +1405,7 @@
     "Optional notes...": "Optional notes...",
     "Optional remarks": "Optional remarks",
     "Optional remarks...": "Optional remarks...",
+    "Optional. If you fill in any field, all fields below become required.": "Optional. If you fill in any field, all fields below become required.",
     "Or Choose Custom Date": "Or Choose Custom Date",
     "Order Details": "Order Details",
     "Order Info": "Order Info",
@@ -1536,6 +1538,7 @@
     "Please check the form for errors.": "Please check the form for errors.",
     "Please confirm the details below": "Please confirm the details below",
     "Please enter Webhook URL first.": "Please enter Webhook URL first.",
+    "Please enter a valid ECPay e-invoice notification email.": "Please enter a valid ECPay e-invoice notification email.",
     "Please enter address first": "Please enter address first",
     "Please enter configuration name": "Please enter configuration name",
     "Please enter machine flavor": "Please enter machine flavor",
diff --git a/lang/ja.json b/lang/ja.json
index 9ba9716..2b11923 100644
--- a/lang/ja.json
+++ b/lang/ja.json
@@ -609,6 +609,7 @@
     "EASY_MERCHANT_ID": "EASY_MERCHANT_ID (悠遊付)",
     "ECPay Invoice": "ECPay 電子領収書",
     "ECPay Invoice Settings Description": "ECPay 電子領収書設定",
+    "ECPay e-invoice is optional, but once any field is filled, Store ID / Hash Key / Hash IV / Email are all required.": "ECPay 電子インボイスは任意ですが、いずれかの項目を入力した場合は、店舗 ID / Hash Key / Hash IV / Email がすべて必須になります。",
     "ECPay has no such invoice; marked as pending re-issue": "ECPay has no such invoice; marked as pending re-issue",
     "ECPay query failed": "ECPay query failed",
     "ESUN": "玉山銀行",
@@ -1404,6 +1405,7 @@
     "Optional notes...": "任意のメモ...",
     "Optional remarks": "任意の備考",
     "Optional remarks...": "任意の備考...",
+    "Optional. If you fill in any field, all fields below become required.": "任意。いずれかの項目を入力すると、以下のすべての項目が必須になります。",
     "Or Choose Custom Date": "または日付を選択",
     "Order Details": "注文詳細",
     "Order Info": "注文情報",
@@ -1536,6 +1538,7 @@
     "Please check the form for errors.": "フォームのエラーを確認してください。",
     "Please confirm the details below": "以下の詳細を確認してください",
     "Please enter Webhook URL first.": "最初にWebhook URLを入力してください。",
+    "Please enter a valid ECPay e-invoice notification email.": "有効な ECPay 電子インボイス通知用メールアドレスを入力してください。",
     "Please enter address first": "先に住所を入力してください",
     "Please enter configuration name": "設定名を入力してください",
     "Please enter machine flavor": "機台フレーバーを入力してください",
diff --git a/lang/zh_TW.json b/lang/zh_TW.json
index ef72f1b..711715e 100644
--- a/lang/zh_TW.json
+++ b/lang/zh_TW.json
@@ -609,6 +609,7 @@
     "EASY_MERCHANT_ID": "EASY_MERCHANT_ID (悠遊付)",
     "ECPay Invoice": "綠界電子發票",
     "ECPay Invoice Settings Description": "綠界科技電子發票設定",
+    "ECPay e-invoice is optional, but once any field is filled, Store ID / Hash Key / Hash IV / Email are all required.": "綠界電子發票為選填,但只要填寫任一欄位,特店 ID / Hash Key / Hash IV / Email 即全部必填。",
     "ECPay has no such invoice; marked as pending re-issue": "綠界查無此發票，已標記為待補開",
     "ECPay query failed": "綠界查詢失敗",
     "ESUN": "玉山銀行",
@@ -1404,6 +1405,7 @@
     "Optional notes...": "備註內容（選填）...",
     "Optional remarks": "選填備註",
     "Optional remarks...": "選填備註...",
+    "Optional. If you fill in any field, all fields below become required.": "選填。只要填寫任一欄位,以下欄位即全部必填。",
     "Or Choose Custom Date": "或選擇自訂日期",
     "Order Details": "訂單詳情",
     "Order Info": "單據資訊",
@@ -1536,6 +1538,7 @@
     "Please check the form for errors.": "請檢查欄位內容是否正確。",
     "Please confirm the details below": "請確認以下詳細資訊",
     "Please enter Webhook URL first.": "請先輸入 Webhook 網址。",
+    "Please enter a valid ECPay e-invoice notification email.": "請輸入有效的綠界電子發票通知 Email。",
     "Please enter address first": "請先輸入地址",
     "Please enter configuration name": "請輸入設定名稱",
     "Please enter machine flavor": "請輸入機台風味",
diff --git a/resources/views/admin/basic-settings/payment-configs/create.blade.php b/resources/views/admin/basic-settings/payment-configs/create.blade.php
index fd7fdb4..94385c9 100644
--- a/resources/views/admin/basic-settings/payment-configs/create.blade.php
+++ b/resources/views/admin/basic-settings/payment-configs/create.blade.php
@@ -98,22 +98,27 @@
                         </div>
                     </div>
 
-                    <div class="space-y-6">
+                    <div class="space-y-6" x-data="{ vals: { store_id: '', hash_key: '', hash_iv: '', email: '' }, get anyFilled() { return Object.values(this.vals).some(v => (v || '').trim() !== '') } }">
+                        <p class="text-[11px] font-bold text-slate-400 leading-relaxed -mt-2">{{ __('Optional. If you fill in any field, all fields below become required.') }}</p>
                         <div>
-                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice Store ID') }}</label>
-                            <input type="text" name="settings[ecpay_invoice][store_id]" class="luxury-input w-full">
+                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice Store ID') }}<span x-show="anyFilled" class="text-rose-500 ml-0.5">*</span></label>
+                            <input type="text" name="settings[ecpay_invoice][store_id]" x-model="vals.store_id" class="luxury-input w-full">
+                            @error('settings.ecpay_invoice.store_id')<p class="mt-1.5 text-[11px] font-bold text-rose-500">{{ $message }}</p>@enderror
                         </div>
                         <div>
-                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice HashKey') }}</label>
-                            <input type="text" name="settings[ecpay_invoice][hash_key]" class="luxury-input w-full">
+                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice HashKey') }}<span x-show="anyFilled" class="text-rose-500 ml-0.5">*</span></label>
+                            <input type="text" name="settings[ecpay_invoice][hash_key]" x-model="vals.hash_key" class="luxury-input w-full">
+                            @error('settings.ecpay_invoice.hash_key')<p class="mt-1.5 text-[11px] font-bold text-rose-500">{{ $message }}</p>@enderror
                         </div>
                         <div>
-                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice HashIV') }}</label>
-                            <input type="text" name="settings[ecpay_invoice][hash_iv]" class="luxury-input w-full">
+                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice HashIV') }}<span x-show="anyFilled" class="text-rose-500 ml-0.5">*</span></label>
+                            <input type="text" name="settings[ecpay_invoice][hash_iv]" x-model="vals.hash_iv" class="luxury-input w-full">
+                            @error('settings.ecpay_invoice.hash_iv')<p class="mt-1.5 text-[11px] font-bold text-rose-500">{{ $message }}</p>@enderror
                         </div>
                         <div>
-                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice Notification Email') }}</label>
-                            <input type="text" name="settings[ecpay_invoice][email]" class="luxury-input w-full">
+                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice Notification Email') }}<span x-show="anyFilled" class="text-rose-500 ml-0.5">*</span></label>
+                            <input type="text" name="settings[ecpay_invoice][email]" x-model="vals.email" class="luxury-input w-full">
+                            @error('settings.ecpay_invoice.email')<p class="mt-1.5 text-[11px] font-bold text-rose-500">{{ $message }}</p>@enderror
                         </div>
                     </div>
                 </div>
diff --git a/resources/views/admin/basic-settings/payment-configs/edit.blade.php b/resources/views/admin/basic-settings/payment-configs/edit.blade.php
index f489773..b3ed426 100644
--- a/resources/views/admin/basic-settings/payment-configs/edit.blade.php
+++ b/resources/views/admin/basic-settings/payment-configs/edit.blade.php
@@ -102,22 +102,27 @@
                         </div>
                     </div>
 
-                    <div class="space-y-6">
+                    <div class="space-y-6" x-data="{ vals: { store_id: @js($settings['ecpay_invoice']['store_id'] ?? ''), hash_key: @js($settings['ecpay_invoice']['hash_key'] ?? ''), hash_iv: @js($settings['ecpay_invoice']['hash_iv'] ?? ''), email: @js($settings['ecpay_invoice']['email'] ?? '') }, get anyFilled() { return Object.values(this.vals).some(v => (v || '').trim() !== '') } }">
+                        <p class="text-[11px] font-bold text-slate-400 leading-relaxed -mt-2">{{ __('Optional. If you fill in any field, all fields below become required.') }}</p>
                         <div>
-                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice Store ID') }}</label>
-                            <input type="text" name="settings[ecpay_invoice][store_id]" value="{{ $settings['ecpay_invoice']['store_id'] ?? '' }}" class="luxury-input w-full">
+                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice Store ID') }}<span x-show="anyFilled" class="text-rose-500 ml-0.5">*</span></label>
+                            <input type="text" name="settings[ecpay_invoice][store_id]" x-model="vals.store_id" value="{{ $settings['ecpay_invoice']['store_id'] ?? '' }}" class="luxury-input w-full">
+                            @error('settings.ecpay_invoice.store_id')<p class="mt-1.5 text-[11px] font-bold text-rose-500">{{ $message }}</p>@enderror
                         </div>
                         <div>
-                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice HashKey') }}</label>
-                            <input type="text" name="settings[ecpay_invoice][hash_key]" value="{{ $settings['ecpay_invoice']['hash_key'] ?? '' }}" class="luxury-input w-full">
+                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice HashKey') }}<span x-show="anyFilled" class="text-rose-500 ml-0.5">*</span></label>
+                            <input type="text" name="settings[ecpay_invoice][hash_key]" x-model="vals.hash_key" value="{{ $settings['ecpay_invoice']['hash_key'] ?? '' }}" class="luxury-input w-full">
+                            @error('settings.ecpay_invoice.hash_key')<p class="mt-1.5 text-[11px] font-bold text-rose-500">{{ $message }}</p>@enderror
                         </div>
                         <div>
-                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice HashIV') }}</label>
-                            <input type="text" name="settings[ecpay_invoice][hash_iv]" value="{{ $settings['ecpay_invoice']['hash_iv'] ?? '' }}" class="luxury-input w-full">
+                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice HashIV') }}<span x-show="anyFilled" class="text-rose-500 ml-0.5">*</span></label>
+                            <input type="text" name="settings[ecpay_invoice][hash_iv]" x-model="vals.hash_iv" value="{{ $settings['ecpay_invoice']['hash_iv'] ?? '' }}" class="luxury-input w-full">
+                            @error('settings.ecpay_invoice.hash_iv')<p class="mt-1.5 text-[11px] font-bold text-rose-500">{{ $message }}</p>@enderror
                         </div>
                         <div>
-                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice Notification Email') }}</label>
-                            <input type="text" name="settings[ecpay_invoice][email]" value="{{ $settings['ecpay_invoice']['email'] ?? '' }}" class="luxury-input w-full">
+                            <label class="block text-[11px] font-black text-slate-400 uppercase tracking-[0.2em] mb-2">{{ __('Invoice Notification Email') }}<span x-show="anyFilled" class="text-rose-500 ml-0.5">*</span></label>
+                            <input type="text" name="settings[ecpay_invoice][email]" x-model="vals.email" value="{{ $settings['ecpay_invoice']['email'] ?? '' }}" class="luxury-input w-full">
+                            @error('settings.ecpay_invoice.email')<p class="mt-1.5 text-[11px] font-bold text-rose-500">{{ $message }}</p>@enderror
                         </div>
                     </div>
                 </div>