diff --git a/docs/qa/payment-link.postman_collection.json b/docs/qa/payment-link.postman_collection.json
index ad712e6..c64b10c 100644
--- a/docs/qa/payment-link.postman_collection.json
+++ b/docs/qa/payment-link.postman_collection.json
@@ -22,7 +22,7 @@
         "url": { "raw": "{{baseUrl}}/createtransaksi", "host": ["{{baseUrl}}"], "path": ["createtransaksi"] },
         "body": {
           "mode": "raw",
-          "raw": "{\n  \"item_id\": \"order-demo-1\",\n  \"nominal\": 150000,\n  \"customer\": { \"name\": \"Demo User\", \"email\": \"demo@example.com\" },\n  \"allowed_methods\": [\"bank_transfer\", \"credit_card\", \"gopay\", \"cstore\"]\n}"
+          "raw": "{\n  \"mercant_id\": \"REFNO-001\",\n  \"timestamp\": 1731300000000,\n  \"deskripsi\": \"Bayar Internet\",\n  \"nominal\": 200000,\n  \"nama\": \"Demo User\",\n  \"no_telepon\": \"081234567890\",\n  \"email\": \"demo@example.com\",\n  \"item\": [\n    { \"item_id\": \"TKG-2511101\", \"nama\": \"Internet\", \"harga\": 200000, \"qty\": 1 }\n  ]\n}"
         }
       },
       "event": [
@@ -33,18 +33,16 @@
             "exec": [
               "let res = {};",
               "try { res = pm.response.json(); } catch(e) { res = {}; }",
-              "if (res && res.token) {",
-              "  pm.collectionVariables.set('token', res.token);",
+              "const url = (res && res.data && res.data.url) ? res.data.url : (res && res.url ? res.url : '');",
+              "if (url) {",
+              "  pm.collectionVariables.set('paymentLinkUrl', url);",
+              "  const trimmed = url.replace(/\\\/$/, '');",
+              "  const parts = trimmed.split('/');",
+              "  const tok = parts[parts.length - 1];",
+              "  pm.collectionVariables.set('token', tok);",
               "}",
-              "if (res && res.order_id) {",
-              "  pm.collectionVariables.set('order_id', res.order_id);",
-              "}",
-              "if (res && res.url) {",
-              "  pm.collectionVariables.set('paymentLinkUrl', res.url);",
-              "}",
-              "pm.test('Create Transaction returns token and order_id', function () {",
-              "  pm.expect(res.token, 'token exists').to.be.a('string');",
-              "  pm.expect(res.order_id, 'order_id exists').to.be.a('string');",
+              "pm.test('Create Transaction returns data.url and token', function () {",
+              "  pm.expect(url, 'data.url exists').to.be.a('string');",
               "});"
             ]
           }
@@ -77,6 +75,7 @@
             "exec": [
               "let res = {};",
               "try { res = pm.response.json(); } catch(e) { res = {}; }",
+              "if (res && res.order_id) { pm.collectionVariables.set('order_id', res.order_id); }",
               "pm.test('Resolve Token payload has order_id and nominal', function () {",
               "  pm.expect(res.order_id, 'order_id').to.be.a('string');",
               "  pm.expect(res.nominal, 'nominal').to.exist;",
diff --git a/docs/sprint-change-proposal.md b/docs/sprint-change-proposal.md
index d3073a1..dd25fba 100644
--- a/docs/sprint-change-proposal.md
+++ b/docs/sprint-change-proposal.md
@@ -36,7 +36,7 @@
     ]
   }
   ```
-- Mapping `order_id`: gunakan `item[0].item_id` sebagai `order_id` untuk Midtrans (validasi format/unik per transaksi aktif).
+  - Mapping `order_id`: gunakan `"mercant_id:item_id"` bila keduanya tersedia (contoh: `MERC-001:ITEM-12345`). Jika salah satu tidak ada, fallback ke `item[0].item_id` atau `mercant_id`. Tujuan: item yang sama pada merchant berbeda tetap menghasilkan order unik sehingga link bisa diterbitkan.
 - Idempotensi: jika `order_id` + `nominal` sama dan status transaksi masih `pending`, kembalikan payment link sebelumnya; jika `nominal` berbeda, kembalikan `422 AMOUNT_MISMATCH`.
 - Response (sukses):
   ```json
diff --git a/server/index.cjs b/server/index.cjs
index b014f6f..da71cc1 100644
--- a/server/index.cjs
+++ b/server/index.cjs
@@ -207,6 +207,30 @@ app.post('/api/payments/charge', async (req, res) => {
     const pt = req?.body?.payment_type
     logInfo('charge.request', { id: req.id, payment_type: pt })
     logDebug('charge.payload', maskPayload(req.body))
+
+    // Idempotency guard: if an order is already pending in Midtrans, block re-charge for the same order_id
+    const orderId = req?.body?.transaction_details?.order_id || req?.body?.order_id || ''
+    if (orderId) {
+      try {
+        const st = await core.transaction.status(orderId)
+        const ts = (st?.transaction_status || '').toLowerCase()
+        if (ts === 'pending') {
+          logWarn('charge.blocked.pending_exists', { id: req.id, order_id: orderId })
+          return res.status(409).json({
+            error: 'ORDER_ACTIVE',
+            message: 'Order sudah memiliki transaksi pending di Midtrans; tidak dapat membuat ulang. Gunakan instruksi pembayaran yang ada atau buat order baru.',
+            status: st,
+          })
+        }
+      } catch (e) {
+        const msg = (e?.message || '').toLowerCase()
+        if (msg.includes('not found') || msg.includes('404')) {
+          logDebug('charge.status_not_found', { order_id: orderId })
+        } else {
+          logDebug('charge.status_check_error', { order_id: orderId, message: e?.message })
+        }
+      }
+    }
     const isBankType = pt === 'bank_transfer' || pt === 'echannel' || pt === 'permata'
     if (isBankType && !ENABLE.bank_transfer) {
       logWarn('charge.blocked', { id: req.id, reason: 'bank_transfer disabled' })
@@ -251,7 +275,7 @@ app.get('/api/payments/:orderId/status', async (req, res) => {
 })
 
 // External ERP Create Transaction → issue payment link
-app.post('/createtransaksi', (req, res) => {
+app.post('/createtransaksi', async (req, res) => {
   try {
     if (!verifyExternalKey(req)) {
       logWarn('createtransaksi.unauthorized', { id: req.id })
@@ -268,7 +292,12 @@ app.post('/createtransaksi', (req, res) => {
     const nominalRaw = req?.body?.nominal
     const items = Array.isArray(req?.body?.item) ? req.body.item : []
     const primaryItemId = items?.[0]?.item_id
-    const order_id = String(primaryItemId || mercantId || req?.body?.order_id || req?.body?.item_id || '')
+    // Mapping order_id: gunakan "mercant_id:item_id" bila keduanya tersedia,
+    // jika tidak, fallback ke item_id atau mercant_id atau field order_id/item_id yang disediakan.
+    const order_id = String(
+      (primaryItemId && mercantId) ? `${mercantId}:${primaryItemId}` :
+      (primaryItemId || mercantId || req?.body?.order_id || req?.body?.item_id || '')
+    )
 
     // Bentuk customer dari field nama/no_telepon/email
     const customer = {
@@ -299,6 +328,28 @@ app.post('/createtransaksi', (req, res) => {
       return res.status(409).json({ error: 'ORDER_ACTIVE', message: 'Active payment link exists' })
     }
 
+    // Guard tambahan: cek ke Midtrans apakah order_id sudah memiliki transaksi pending
+    try {
+      const status = await core.transaction.status(order_id)
+      const s = (status?.transaction_status || '').toLowerCase()
+      if (s === 'pending') {
+        logWarn('createtransaksi.midtrans_pending', { order_id })
+        return res.status(409).json({
+          error: 'ORDER_ACTIVE',
+          message: 'Order sudah memiliki transaksi pending di Midtrans; gunakan instruksi pembayaran yang ada atau buat order baru.',
+          status: { order_id: status?.order_id, status_code: status?.status_code, status_message: status?.status_message, payment_type: status?.payment_type },
+        })
+      }
+    } catch (e) {
+      // Jika 404/not found, lanjut membuat payment link; error lain tetap diteruskan
+      const msg = (e?.message || '').toLowerCase()
+      if (msg.includes('not found') || msg.includes('404')) {
+        logDebug('createtransaksi.midtrans_status_not_found', { order_id })
+      } else {
+        logDebug('createtransaksi.midtrans_status_check_error', { order_id, message: e?.message })
+      }
+    }
+
     const token = createPaymentLinkToken({ order_id, nominal, expire_at, customer, allowed_methods })
     const url = `${PAYMENT_LINK_BASE}/${token}`
     activeOrders.set(order_id, expire_at)
diff --git a/tmp-createtransaksi.json b/tmp-createtransaksi.json
new file mode 100644
index 0000000..49d2134
--- /dev/null
+++ b/tmp-createtransaksi.json
@@ -0,0 +1,12 @@
+{
+  "mercant_id": "REFNO-001",
+  "timestamp": 1731300000000,
+  "deskripsi": "Bayar Internet",
+  "nominal": 200000,
+  "nama": "Demo User",
+  "no_telepon": "081234567890",
+  "email": "demo@example.com",
+  "item": [
+    { "item_id": "TKG-2511131", "nama": "Internet", "harga": 200000, "qty": 1 }
+  ]
+}