diff --git a/assets/js/credits.js b/assets/js/credits.js
index 582638fd..1cff6d57 100644
--- a/assets/js/credits.js
+++ b/assets/js/credits.js
@@ -457,7 +457,9 @@
 				headers: { 'Idempotency-Key': operationKey(form) },
 				body: JSON.stringify({
 					package: pkg,
-					custom_price: custom,
+					// 预设档位路径不消费该字段；送空串会被 REST 的 pattern 拒绝
+					// （WP 仅在键缺失时应用 default），故非自定义金额时显式送 '0'。
+					custom_price: validCustom ? custom : '0',
 					payment_method: method
 				})
 			}).then(function (r) {
diff --git a/src/Credits/BalanceServiceRest.php b/src/Credits/BalanceServiceRest.php
index 56a10b3b..fb735666 100644
--- a/src/Credits/BalanceServiceRest.php
+++ b/src/Credits/BalanceServiceRest.php
@@ -30,7 +30,10 @@ trait BalanceServiceRest {
 				'permission_callback' => [$this, 'check_asset_rest'],
 				'args' => [
 					'package' => ['type' => 'string', 'default' => 'custom', 'sanitize_callback' => 'sanitize_text_field'],
-					'custom_price' => ['type' => 'string', 'default' => '0', 'pattern' => '^(0|[1-9]\\d*)(?:\\.\\d{1,2})?$'],
+					// 选中预设档位时 custom_price 无意义，但前端仍会带上该键（空串或不存在），
+					// 而 WP REST 只在「键缺失」时应用 default，空串会直接进 pattern 校验，
+					// 因此模式必须显式放行空串，否则报 rest_invalid_param（无效参数：custom_price）。
+					'custom_price' => ['type' => 'string', 'default' => '0', 'pattern' => '^(?:(?:0|[1-9]\\d*)(?:\\.\\d{1,2})?)?$'],
 					'payment_method' => ['type' => 'string', 'required' => true, 'sanitize_callback' => 'sanitize_key'],
 				],
 			],
@@ -142,7 +145,11 @@ trait BalanceServiceRest {
 			$params = $request->get_params();
 		}
 		$package_key    = sanitize_text_field((string) ($params['package'] ?? 'custom'));
-		$custom_price   = isset($params['custom_price']) ? (string) $params['custom_price'] : '0';
+		// 空串与键缺失等价（预设档位路径不消费本字段），归一化为 '0' 以对齐参数声明的 default。
+		$custom_price   = trim((string) ($params['custom_price'] ?? ''));
+		if ($custom_price === '') {
+			$custom_price = '0';
+		}
 		$payment_method = sanitize_key((string) ($params['payment_method'] ?? 'alipay'));
 
 		$result = $this->create_charge_order($user_id, $package_key, $custom_price, $payment_method, $operation_key);
diff --git a/tests/widget-system/asset-ledger-contract.test.cjs b/tests/widget-system/asset-ledger-contract.test.cjs
index 8b3bb079..f70be396 100644
--- a/tests/widget-system/asset-ledger-contract.test.cjs
+++ b/tests/widget-system/asset-ledger-contract.test.cjs
@@ -290,6 +290,30 @@ test('asset purchases share the order center and refresh every wallet surface',
   assert.match(balanceRest, /'order_number'\s*=>\s*\$order_number/)
   assert.match(chargeCard, /self::TYPE_CREDITS[\s\S]*?ORDER_PRODUCT_POINTS/)
 
+  // 选中预设档位时 custom_price 既可能「键存在但值为空串」（自定义输入框存在但未填），
+  // 也可能根本不存在于表单（后台关闭了自定义金额）。WP REST 仅在键缺失时应用 default，
+  // 空串会被送进 pattern 校验并被拒，表现为 rest_invalid_param「无效参数：custom_price」。
+  // 因此：模式必须放行空串，回调必须把空串归一化为声明的 default，前端必须显式送 '0'。
+  //
+  // 注意：不要拿含反斜杠的整串去 includes()——JS 字面量与 PHP 单引号串的转义层数不同，
+  // 会静默比对失败。这里拆成不含反斜杠的片段断言，语义等价且与转义层数无关。
+  assert.ok(
+    balanceRest.includes("'pattern' => '^(?:(?:0|[1-9]"),
+    'custom_price pattern must be optional (the old bare pattern rejected the empty string)',
+  )
+  assert.ok(
+    balanceRest.includes("{1,2})?)?$'"),
+    'custom_price pattern must allow the empty string so preset packages pass validation',
+  )
+  assert.ok(
+    balanceRest.includes("if ($custom_price === '') {"),
+    'rest_charge_create must normalise an empty custom_price to the declared default',
+  )
+  assert.ok(
+    creditsJs.includes("custom_price: validCustom ? custom : '0',"),
+    'balance charge must send 0 rather than an empty string when a preset package is selected',
+  )
+
   assert.match(creditsJs, /function refreshAssetBalances\(/)
   assert.match(creditsJs, /querySelectorAll\('\[data-aksrt-wallet-value\]'/)
   assert.match(creditsJs, /querySelectorAll\('\[data-aksrt-points-value\]'/)