diff --git a/backend/src/routes/adminExpenses.js b/backend/src/routes/adminExpenses.js
index 8c6c761a..a79923f5 100644
--- a/backend/src/routes/adminExpenses.js
+++ b/backend/src/routes/adminExpenses.js
@@ -220,4 +220,23 @@ router.patch('/:id', requireExpenses, requirePermission('accounting.manage'),
     return successResponse(res, { expense });
   }));
 
+// Add an expense onto a client invoice -> marks it invoiced (locks editing).
+router.post('/:id/invoice', requireExpenses, requirePermission('accounting.manage'),
+  [param('id').isInt({ min: 1 }), body('customerAccountId').isInt({ min: 1 }),
+    body('eventId').optional({ nullable: true }).isInt({ min: 1 }), body('contractId').optional({ nullable: true }).isInt({ min: 1 }),
+    body('markupType').optional().isIn(expenseService.MARKUP_TYPES)],
+  handleAsync(async (req, res) => {
+    validateRequest(req);
+    return successResponse(res, await expenseService.rebillExpense(toInt(req.params.id), req.body, req.admin.id), 201, 'Expense invoiced');
+  }));
+
+// Mark an expense paid / settled (manual).
+router.post('/:id/paid', requireExpenses, requirePermission('accounting.manage'),
+  [param('id').isInt({ min: 1 }), body('paid').isBoolean(), body('paymentMethod').optional({ nullable: true }).isIn(expenseService.PAYMENT_METHODS)],
+  handleAsync(async (req, res) => {
+    validateRequest(req);
+    const expense = await expenseService.markExpensePaid(toInt(req.params.id), req.body, req.admin.id);
+    return successResponse(res, { expense });
+  }));
+
 module.exports = router;
diff --git a/backend/src/routes/adminTaxReport.js b/backend/src/routes/adminTaxReport.js
index af3a29fd..dff08597 100644
--- a/backend/src/routes/adminTaxReport.js
+++ b/backend/src/routes/adminTaxReport.js
@@ -8,9 +8,11 @@
  *   GET /pdf       → landscape A4 PDF, Content-Disposition: attachment
  *   GET /csv       → RFC-4180 CSV, Content-Disposition: attachment
  *
- * Reuses the existing `bills` feature flag + `bills.view` permission.
- * Tax data is just a different lens on invoice data — admins who can
- * read invoices can read the tax report; no new RBAC surface needed.
+ * Gated by the Accounting master flag + the `taxReport` sub-flag
+ * (independent of `bills` — Tax export was moved out of CRM into
+ * Accounting). Still uses the `bills.view` permission: tax data is just
+ * a different lens on invoice data, so admins who can read invoices can
+ * read the tax report; no new RBAC surface needed.
  */
 
 const express = require('express');
@@ -23,19 +25,19 @@ const { db } = require('../database/db');
 
 const router = express.Router();
 
-// The tax report has its own dedicated flag (taxReport) — independent
-// from `bills` so admins can leave it off until they actually need to
-// run the export. The frontend mirrors the dependency rule (bills off
-// → taxReport off) but we re-check both server-side for defence in
-// depth.
+// The tax report now lives under the Accounting master flag and has its
+// own dedicated `taxReport` sub-flag — it is INDEPENDENT of `bills`
+// (Tax export was moved permanently out of CRM into Accounting). The
+// frontend mirrors the dependency rule (accounting off → taxReport off)
+// but we re-check both server-side for defence in depth.
 async function requireTaxReportFlag(req, res, next) {
   try {
-    const rows = await db('feature_flags').whereIn('key', ['bills', 'taxReport']).select('key', 'value');
+    const rows = await db('feature_flags').whereIn('key', ['accounting', 'taxReport']).select('key', 'value');
     const isOn = (row) => row && (row.value === true || row.value === 1 || row.value === '1');
-    const bills      = isOn(rows.find((r) => r.key === 'bills'));
+    const accounting = isOn(rows.find((r) => r.key === 'accounting'));
     const taxReport  = isOn(rows.find((r) => r.key === 'taxReport'));
-    if (!bills) {
-      return res.status(403).json({ error: 'Bills feature is disabled', code: 'BILLS_DISABLED' });
+    if (!accounting) {
+      return res.status(403).json({ error: 'Accounting feature is disabled', code: 'ACCOUNTING_DISABLED' });
     }
     if (!taxReport) {
       return res.status(403).json({ error: 'Tax report feature is disabled', code: 'TAX_REPORT_DISABLED' });
diff --git a/backend/src/services/expenseService.js b/backend/src/services/expenseService.js
index 0157d0b8..fdff8ab6 100644
--- a/backend/src/services/expenseService.js
+++ b/backend/src/services/expenseService.js
@@ -337,6 +337,14 @@ function transformExpense(row) {
     receiptPath: row.receipt_path,
     hasProof: !!row.receipt_path,
     taxTreatment: row.tax_treatment,
+    // invoiced = added to a real client invoice (locks editing); paid = settled.
+    billedInvoiceId: row.billed_invoice_id,
+    billedInvoiceLineItemId: row.billed_invoice_line_item_id,
+    invoiced: !!row.billed_invoice_id,
+    customerAccountId: row.customer_account_id,
+    paid: !!row.supplier_paid,
+    paidAt: row.supplier_paid_at,
+    paymentMethod: row.payment_method,
     status: row.status,
     createdAt: row.created_at,
     updatedAt: row.updated_at,
@@ -422,7 +430,10 @@ const EXPENSE_EDITABLE = {
 };
 
 async function updateExpense(id, payload, adminId, { receiptPath } = {}) {
-  await getExpense(id);
+  const existing = await getExpense(id);
+  if (existing.invoiced) {
+    throw new AppError('Expense is invoiced — editing is locked', 409, 'EXPENSE_LOCKED');
+  }
   const patch = { updated_at: new Date() };
   for (const [camel, snake] of Object.entries(EXPENSE_EDITABLE)) {
     if (payload[camel] !== undefined) patch[snake] = payload[camel] === '' ? null : payload[camel];
@@ -433,8 +444,70 @@ async function updateExpense(id, payload, adminId, { receiptPath } = {}) {
   return getExpense(id);
 }
 
+/** Add an internal expense onto a client invoice (mints a line). Marks it
+ *  invoiced (locks editing) + links the invoice. base = chf amount + markup. */
+async function rebillExpense(id, payload, adminId, trx0) {
+  const run = async (trx) => {
+    const row = await trx('expenses').where({ id }).first();
+    if (!row) throw new AppError('Expense not found', 404, 'EXPENSE_NOT_FOUND');
+    const exp = transformExpense(row);
+    if (exp.invoiced) throw new AppError('Expense already invoiced', 409, 'ALREADY_INVOICED');
+    if (!payload.customerAccountId) throw new AppError('customerAccountId is required', 400, 'CUSTOMER_REQUIRED');
+    const base = exp.chfAmountMinor;
+    if (base == null) throw new AppError('Expense has no amount to invoice', 400, 'AMOUNT_REQUIRED');
+    const markup = await resolveMarkup(
+      { markupType: row.markup_type, markupPercent: row.markup_percent, markupFlatMinor: row.markup_flat_minor },
+      payload, payload.contractId, trx,
+    );
+    const lineTotal = base + computeMarkupMinor(base, markup);
+    const label = exp.description || exp.supplierName || 'Aufwand';
+    const { invoiceIds } = await invoiceService.createInvoice({
+      customerAccountId: payload.customerAccountId,
+      eventId: payload.eventId || exp.eventId || null,
+      lineItems: [{ description: `${label} (Weiterverrechnung)`, quantity: 1, unit_price_minor: lineTotal, discount_percent: 0, line_total_minor: lineTotal }],
+    }, adminId, trx);
+    const invoiceId = Array.isArray(invoiceIds) ? invoiceIds[0] : null;
+    if (!invoiceId) throw new AppError('Failed to create invoice', 500, 'INVOICE_FAILED');
+    const line = await trx('invoice_line_items').where({ invoice_id: invoiceId }).orderBy('id', 'desc').first('id');
+    await trx('expenses').where({ id }).update({
+      billed_invoice_id: invoiceId,
+      billed_invoice_line_item_id: line ? line.id : null,
+      billed_at: new Date(),
+      customer_account_id: payload.customerAccountId,
+      markup_type: markup.type,
+      markup_percent: markup.type === 'percent' ? markup.percent : null,
+      markup_flat_minor: markup.type === 'flat' ? markup.flatMinor : null,
+      status: 'invoiced',
+      updated_at: new Date(),
+    });
+    await logActivity('expense_invoiced', { expenseId: id, invoiceId }, adminId);
+    return invoiceId;
+  };
+  const invoiceId = trx0 ? await run(trx0) : await db.transaction(run);
+  return { expense: await getExpense(id), invoiceId };
+}
+
+/** Mark an expense paid/settled (manual). */
+async function markExpensePaid(id, { paid, paidAt, paymentMethod, paymentReference }, adminId) {
+  await getExpense(id);
+  if (paymentMethod && !PAYMENT_METHODS.includes(paymentMethod)) {
+    throw new AppError(`paymentMethod must be one of ${PAYMENT_METHODS.join(', ')}`, 400, 'BAD_PAYMENT_METHOD');
+  }
+  await db('expenses').where({ id }).update({
+    supplier_paid: !!paid,
+    supplier_paid_at: paid ? (paidAt ? new Date(paidAt) : new Date()) : null,
+    payment_method: paid ? (paymentMethod || null) : null,
+    payment_reference: paid ? (paymentReference || null) : null,
+    updated_at: new Date(),
+  });
+  await logActivity('expense_paid', { expenseId: id, paid: !!paid }, adminId);
+  return getExpense(id);
+}
+
 module.exports = {
   getAccountingSettings,
+  rebillExpense,
+  markExpensePaid,
   // incoming invoices
   recordInboundDocument,
   getInbound,