diff --git a/assets/js/credits.js b/assets/js/credits.js
index 582638fd..2280e585 100644
--- a/assets/js/credits.js
+++ b/assets/js/credits.js
@@ -355,12 +355,18 @@
 		});
 		// Zibll data-for/data-value 选中模型：余额档位（.vip-product.product-box）
 		// 选中变化不产生 change 事件（隐藏 input 由程序赋值），需显式重置幂等键。
+		var customInput = modal.querySelector('input[name="custom_price"]');
 		function selectProduct(value) {
 			modal.querySelectorAll('[data-for="balance_product"]').forEach(function (el) {
 				el.classList.toggle('active', el.getAttribute('data-value') === value);
 			});
 			var hidden = modal.querySelector('input[name="balance_product"]');
 			if (hidden) hidden.value = value;
+			// 选中预设档位即代表放弃自定义金额：清空输入框，否则框里残留的数字会在
+			// 提交时按「合法自定义金额」把 package 顶回 custom，静默覆盖刚点的档位。
+			if (value !== 'custom' && customInput) {
+				customInput.value = '';
+			}
 			if (form) resetOperationKey(form);
 		}
 		modal.querySelectorAll('[data-for="balance_product"]').forEach(function (el) {
@@ -368,7 +374,6 @@
 				selectProduct(el.getAttribute('data-value'));
 			});
 		});
-		var customInput = modal.querySelector('input[name="custom_price"]');
 		if (customInput) {
 			customInput.addEventListener('input', function () {
 				if (String(customInput.value || '').trim() !== '') {
@@ -444,12 +449,6 @@
 				notyf('请选择或输入充值金额', 'danger');
 				return;
 			}
-			var methodEl = form.querySelector('input[name="payment_method"]');
-			var method = methodEl ? methodEl.value : '';
-			if (!method) {
-				notyf('暂无可用支付方式', 'danger');
-				return;
-			}
 			busy = true;
 			notyf('正在创建充值订单…', 'load', '', 'aksrt-balance-charge-toast');
 			api('/pay/balance/charge', {
@@ -457,6 +456,8 @@
 				headers: { 'Idempotency-Key': operationKey(form) },
 				body: JSON.stringify({
 					package: pkg,
+					// 预设档位下该字段为空串：服务端仅在 package=custom 时消费它，
+					// 空串表示「未使用自定义金额」，不是非法值。
 					custom_price: custom,
 					payment_method: method
 				})
diff --git a/src/Credits/BalanceServiceRest.php b/src/Credits/BalanceServiceRest.php
index 56a10b3b..0ff7be39 100644
--- a/src/Credits/BalanceServiceRest.php
+++ b/src/Credits/BalanceServiceRest.php
@@ -30,7 +30,13 @@ trait BalanceServiceRest {
 				'permission_callback' => [$this, 'check_asset_rest'],
 				'args' => [
 					'package' => ['type' => 'string', 'default' => 'custom', 'sanitize_callback' => 'sanitize_text_field'],
-					'custom_price' => ['type' => 'string', 'default' => '0', 'pattern' => '^(0|[1-9]\\d*)(?:\\.\\d{1,2})?$'],
+					// 仅 package=custom 时被消费；选预设档位时前端送空串，空串即
+					//「未使用自定义金额」，属正常取值而非非法值。金额格式与区间的
+					// 唯一裁决在 create_charge_order()（AssetAmount::balance + custom_limit），
+					// 这里再挂一份 pattern 会形成第二套口径：WP 的 default 只在键缺失时
+					// 生效，键存在而值为空串时 pattern 会直接判失败，把预设档位误报为
+					// rest_invalid_param（无效参数：custom_price）。
+					'custom_price' => ['type' => 'string', 'default' => '', 'sanitize_callback' => 'sanitize_text_field'],
 					'payment_method' => ['type' => 'string', 'required' => true, 'sanitize_callback' => 'sanitize_key'],
 				],
 			],
@@ -137,13 +143,11 @@ trait BalanceServiceRest {
 		if (is_wp_error($operation_key)) {
 			return $operation_key;
 		}
-		$params  = $request->get_json_params();
-		if (!is_array($params)) {
-			$params = $request->get_params();
-		}
-		$package_key    = sanitize_text_field((string) ($params['package'] ?? 'custom'));
-		$custom_price   = isset($params['custom_price']) ? (string) $params['custom_price'] : '0';
-		$payment_method = sanitize_key((string) ($params['payment_method'] ?? 'alipay'));
+		// 单一取值口径：直接读注册时声明的 args（type / default / sanitize_callback
+		// 均已声明），不再手工重读 JSON 体并复刻一遍清洗逻辑。
+		$package_key    = (string) $request->get_param('package');
+		$custom_price   = (string) $request->get_param('custom_price');
+		$payment_method = (string) $request->get_param('payment_method');
 
 		$result = $this->create_charge_order($user_id, $package_key, $custom_price, $payment_method, $operation_key);
 		if (is_wp_error($result)) {
diff --git a/tests/widget-system/balance-charge-modal.test.cjs b/tests/widget-system/balance-charge-modal.test.cjs
index 3b94b7c8..d6e001ce 100644
--- a/tests/widget-system/balance-charge-modal.test.cjs
+++ b/tests/widget-system/balance-charge-modal.test.cjs
@@ -27,6 +27,7 @@ const read = (...seg) => fs.readFileSync(path.join(root, ...seg), 'utf8');
 const wallet = read('inc', 'helpers', 'user-center-renderers', 'credits-wallet.php');
 const creditsJs = read('assets', 'js', 'credits.js');
 const creditsCss = read('assets', 'css', 'routes', 'user-center', 'credits.css');
+const balanceRest = read('src', 'Credits', 'BalanceServiceRest.php');
 
 test('弹窗壳为 Zibll refresh_modal 同构静态壳并带 data 钩子', () => {
   assert.match(wallet, /class="modal flex jc fade"[^>]*data-aksrt-charge-modal/);
@@ -67,3 +68,53 @@ test('开关自包含：不依赖 jQuery/Bootstrap modal 运行时', () => {
   assert.match(creditsJs, /modal\.style\.display = 'flex'/);
   assert.doesNotMatch(creditsJs, /modal\.style\.display = 'block'/);
 });
+
+/**
+ * 余额充值提交契约（预设档位被 REST 参数层拦截的回归护栏）。
+ *
+ * custom_price 只在 package=custom 时被消费，选中预设档位时前端必带该键且值为
+ * 空串。WP REST 的 default 仅在「键完全缺失」时生效：键存在而值为空串时 default
+ * 不参与，空串直接进 pattern 校验 → 请求在参数层就被拦下（rest_invalid_param
+ * 「无效参数：custom_price」），业务回调根本不执行。
+ *
+ * 因此参数声明只保留 type/default/清洗，金额格式与区间的唯一裁决留在
+ * create_charge_order()（AssetAmount::balance + custom_limit 区间校验）。
+ */
+test('充值请求参数：custom_price 空串放行，金额格式只由业务层裁决', () => {
+  const chargeRoute = balanceRest.slice(
+    balanceRest.indexOf("'/pay/balance/charge'"),
+    balanceRest.indexOf("'/pay/transfer'"),
+  );
+  assert.match(chargeRoute, /'custom_price'\s*=>\s*\['type'\s*=>\s*'string',\s*'default'\s*=>\s*''/);
+  assert.doesNotMatch(
+    chargeRoute,
+    /custom_price'[\s\S]*?'pattern'/,
+    'custom_price must not carry a second amount rule: the empty string is a valid "not applicable" value',
+  );
+
+  const createCallback = balanceRest.slice(
+    balanceRest.indexOf('public function rest_charge_create'),
+    balanceRest.indexOf('public function rest_transfer'),
+  );
+  assert.match(createCallback, /\$custom_price\s*=\s*\(string\) \$request->get_param\('custom_price'\)/);
+  assert.match(createCallback, /\$payment_method\s*=\s*\(string\) \$request->get_param\('payment_method'\)/);
+  // 手工重读请求体会让声明的 default/sanitize_callback 形同虚设（第二套取值口径）。
+  assert.doesNotMatch(createCallback, /get_json_params\(\)|->get_params\(\)/);
+});
+
+test('充值弹窗：选中预设档位清空自定义金额，提交路径无重复读取', () => {
+  // 选中预设档位即放弃自定义金额；否则输入框里残留的数字会在提交时按「合法自定义
+  // 金额」把 package 顶回 custom，用户刚点的档位被静默忽略。
+  assert.match(creditsJs, /if \(value !== 'custom' && customInput\) \{[\s\S]{0,60}customInput\.value = '';/);
+  // 支付方式在提交处理器开头已读取，选档位不会改动它，故充值弹窗内只应存在一处读取
+  // （积分购买弹窗是同构的另一套初始化，各自一处，不在此断言范围）。
+  const chargeInit = creditsJs.slice(
+    creditsJs.indexOf('function initBalanceCharge'),
+    creditsJs.indexOf('function initTransfer'),
+  );
+  assert.strictEqual(
+    [...chargeInit.matchAll(/form\.querySelector\('input\[name="payment_method"\]'\)/g)].length,
+    1,
+    'the submit handler must not re-read payment_method (dead duplicate guard)',
+  );
+});