diff --git a/server/index.cjs b/server/index.cjs
index 34cdcc4..3e11baf 100644
--- a/server/index.cjs
+++ b/server/index.cjs
@@ -338,11 +338,52 @@ app.get('/api/config', (_req, res) => {
   res.json(payload)
 })
 
+// ============================================================================
+// LOG ACCESS AUTHENTICATION (HTTP BASIC AUTH — browser-native login prompt)
+// ============================================================================
+const LOG_BASIC_AUTH_USER = process.env.LOG_BASIC_AUTH_USER || ''
+const LOG_BASIC_AUTH_PASS = process.env.LOG_BASIC_AUTH_PASS || ''
+
+function timingSafeEqualStr(a, b) {
+  const bufA = Buffer.from(String(a))
+  const bufB = Buffer.from(String(b))
+  if (bufA.length !== bufB.length) return false
+  return crypto.timingSafeEqual(bufA, bufB)
+}
+
+function requireLogBasicAuth(req, res, next) {
+  if (!LOG_BASIC_AUTH_USER || !LOG_BASIC_AUTH_PASS) {
+    if (isDevEnv()) return next()
+    logWarn('logs.auth.not_configured', { id: req.id })
+    return res.status(503).json({ error: 'LOG_AUTH_NOT_CONFIGURED', message: 'Set LOG_BASIC_AUTH_USER and LOG_BASIC_AUTH_PASS to enable log access.' })
+  }
+
+  const header = req.headers['authorization'] || ''
+  const [scheme, encoded] = header.split(' ')
+  let user = '', pass = ''
+  if (scheme === 'Basic' && encoded) {
+    try {
+      const decoded = Buffer.from(encoded, 'base64').toString('utf8')
+      const idx = decoded.indexOf(':')
+      user = idx >= 0 ? decoded.slice(0, idx) : decoded
+      pass = idx >= 0 ? decoded.slice(idx + 1) : ''
+    } catch {}
+  }
+
+  const ok = user && pass && timingSafeEqualStr(user, LOG_BASIC_AUTH_USER) && timingSafeEqualStr(pass, LOG_BASIC_AUTH_PASS)
+  if (!ok) {
+    if (scheme === 'Basic') logWarn('logs.auth.failed', { id: req.id, user })
+    res.set('WWW-Authenticate', 'Basic realm="Midtrans Middleware Logs"')
+    return res.status(401).json({ error: 'UNAUTHORIZED', message: 'Login required to access logs' })
+  }
+  next()
+}
+
 /**
  * Get recent logs from memory (dev/debug only)
  * GET /api/logs?limit=100&level=debug|info|warn|error&q=keyword
  */
-app.get('/api/logs', (req, res) => {
+app.get('/api/logs', requireLogBasicAuth, (req, res) => {
   if (!LOG_EXPOSE_API) {
     return res.status(403).json({ error: 'FORBIDDEN', message: 'Log API disabled. Set LOG_EXPOSE_API=true to enable.' })
   }
@@ -365,7 +406,7 @@ app.get('/api/logs', (req, res) => {
  * List all log files in logs directory
  * GET /api/logs/files
  */
-app.get('/api/logs/files', (req, res) => {
+app.get('/api/logs/files', requireLogBasicAuth, (req, res) => {
   if (!LOG_EXPOSE_API) {
     return res.status(403).json({ error: 'FORBIDDEN', message: 'Log API disabled. Set LOG_EXPOSE_API=true to enable.' })
   }
@@ -393,7 +434,7 @@ app.get('/api/logs/files', (req, res) => {
  * Read specific log file
  * GET /api/logs/files/:filename
  */
-app.get('/api/logs/files/:filename', (req, res) => {
+app.get('/api/logs/files/:filename', requireLogBasicAuth, (req, res) => {
   if (!LOG_EXPOSE_API) {
     return res.status(403).json({ error: 'FORBIDDEN', message: 'Log API disabled. Set LOG_EXPOSE_API=true to enable.' })
   }
@@ -504,10 +545,16 @@ app.post('/api/payment-links', async (req, res) => {
     }
 
     // Midtrans order_id only allows alphanumeric characters and - _ ~ . (no ':')
-    const midtransOrderId = order_id.replace(/[^A-Za-z0-9\-_~.]/g, '.')
+    const sanitizedOrderId = order_id.replace(/[^A-Za-z0-9\-_~.]/g, '.')
     // ERP convention: "mercant_id:item_id" — take the segment before ':' as mercant_id for ERP callback matching
     const mercantId = order_id.includes(':') ? order_id.split(':')[0] : order_id
 
+    // Append retry suffix when a previous link for this order expired — Midtrans never allows
+    // reusing an order_id, even an expired one. Keyed by sanitizedOrderId so this stays aligned
+    // with getBaseOrderId(), which strips the retry suffix from what the webhook sends back.
+    const retryCount = orderRetryCount.get(sanitizedOrderId) || 0
+    const midtransOrderId = retryCount > 0 ? `${sanitizedOrderId}.r${retryCount}` : sanitizedOrderId
+
     const customer = {
       name: customerIn.name,
       phone: customerIn.phone,
@@ -521,12 +568,12 @@ app.post('/api/payment-links', async (req, res) => {
       expire_at = now + ttlMin * 60 * 1000
     }
 
-    if (notifiedOrders.has(order_id)) {
+    if (notifiedOrders.has(sanitizedOrderId)) {
       logWarn('payment-links.create.completed', { order_id })
       return res.status(409).json({ error: 'ORDER_COMPLETED', message: 'Order already completed' })
     }
 
-    const existing = activeOrders.get(order_id)
+    const existing = activeOrders.get(sanitizedOrderId)
     if (existing && existing > now) {
       logWarn('payment-links.create.active_exists', { order_id })
       return res.status(409).json({ error: 'ORDER_ACTIVE', message: 'Active payment link exists' })
@@ -552,9 +599,9 @@ app.post('/api/payment-links', async (req, res) => {
 
     const token = createPaymentLinkToken({ order_id: midtransOrderId, nominal, expire_at, customer, allowed_methods })
     const url = `${PAYMENT_LINK_BASE}/${token}`
-    activeOrders.set(order_id, expire_at)
-    orderMerchantId.set(order_id, mercantId)
-    if (midtransOrderId !== order_id) orderMerchantId.set(midtransOrderId, mercantId)
+    activeOrders.set(sanitizedOrderId, expire_at)
+    orderMerchantId.set(sanitizedOrderId, mercantId)
+    if (midtransOrderId !== sanitizedOrderId) orderMerchantId.set(midtransOrderId, mercantId)
 
     logInfo('payment-links.create.issued', { order_id, midtrans_order_id: midtransOrderId, expire_at })
     res.json({ status: '200', messages: 'SUCCESS', data: { url, order_id, midtrans_order_id: midtransOrderId, expire_at } })
@@ -717,20 +764,28 @@ app.post('/createtransaksi', async (req, res) => {
     const items = Array.isArray(req?.body?.item) ? req.body.item : []
     const primaryItemId = items?.[0]?.item_id
 
-    // Midtrans order_id only allows alphanumeric characters and - _ ~ . (no ':')
     const order_id = String(
       (primaryItemId && mercantId) ? `${mercantId}.${primaryItemId}` :
       (primaryItemId || mercantId || req?.body?.order_id || req?.body?.item_id || '')
     )
 
-    // Compute Midtrans-specific order_id — append retry suffix when the previous attempt expired
-    const retryCount = orderRetryCount.get(order_id) || 0
-    const midtransOrderId = retryCount > 0 ? `${order_id}.r${retryCount}` : order_id
+    // Midtrans order_id only allows alphanumeric characters and - _ ~ . (no ':')
+    // order_id may still contain ':' here if it came straight from req.body.order_id/item_id
+    // instead of the mercant_id+item[] branch, so sanitize before it's ever sent to Midtrans.
+    const sanitizedOrderId = order_id.replace(/[^A-Za-z0-9\-_~.]/g, '.')
 
-    if (mercantId) {
+    // Compute Midtrans-specific order_id — append retry suffix when the previous attempt expired.
+    // Keyed by sanitizedOrderId (not the raw order_id) so this stays aligned with getBaseOrderId(),
+    // which strips the retry suffix from the Midtrans-form id the webhook sends back.
+    const retryCount = orderRetryCount.get(sanitizedOrderId) || 0
+    const midtransOrderId = retryCount > 0 ? `${sanitizedOrderId}.r${retryCount}` : sanitizedOrderId
+
+    // ERP convention: "mercant_id:item_id" — fall back to the segment before ':' when mercant_id wasn't sent explicitly
+    const resolvedMercantId = mercantId || (order_id.includes(':') ? order_id.split(':')[0] : '')
+    if (resolvedMercantId) {
       try {
-        orderMerchantId.set(order_id, mercantId)
-        if (midtransOrderId !== order_id) orderMerchantId.set(midtransOrderId, mercantId)
+        orderMerchantId.set(sanitizedOrderId, resolvedMercantId)
+        if (midtransOrderId !== sanitizedOrderId) orderMerchantId.set(midtransOrderId, resolvedMercantId)
       } catch {}
     }
 
@@ -750,12 +805,12 @@ app.post('/createtransaksi', async (req, res) => {
     const ttlMin = PAYMENT_LINK_TTL_MINUTES > 0 ? PAYMENT_LINK_TTL_MINUTES : 1440
     const expire_at = now + ttlMin * 60 * 1000
 
-    if (notifiedOrders.has(order_id)) {
+    if (notifiedOrders.has(sanitizedOrderId)) {
       logWarn('createtransaksi.completed', { order_id })
       return res.status(409).json({ error: 'ORDER_COMPLETED', message: 'Order already completed' })
     }
 
-    const existing = activeOrders.get(order_id)
+    const existing = activeOrders.get(sanitizedOrderId)
     if (existing && existing > now) {
       logWarn('createtransaksi.active_exists', { order_id })
       return res.status(409).json({ error: 'ORDER_ACTIVE', message: 'Active payment link exists' })
@@ -783,7 +838,7 @@ app.post('/createtransaksi', async (req, res) => {
 
     const token = createPaymentLinkToken({ order_id: midtransOrderId, nominal, expire_at, customer, allowed_methods })
     const url = `${PAYMENT_LINK_BASE}/${token}`
-    activeOrders.set(order_id, expire_at)
+    activeOrders.set(sanitizedOrderId, expire_at)
     logInfo('createtransaksi.issued', { order_id, midtrans_order_id: midtransOrderId, retry_count: retryCount, expire_at })
 
     res.json({ status: '200', messages: 'SUCCESS', data: { url } })