diff --git a/backend/routes/customers.js b/backend/routes/customers.js
new file mode 100644
index 0000000..2ee1dcb
--- /dev/null
+++ b/backend/routes/customers.js
@@ -0,0 +1,207 @@
+const express = require('express');
+const { Pool } = require('pg');
+const { v4: uuidv4 } = require('uuid');
+
+const router = express.Router();
+
+// Database pool
+const pool = new Pool({
+  host: process.env.DB_HOST || 'db',
+  port: process.env.DB_PORT || 5432,
+  database: process.env.DB_NAME || 'steuer',
+  user: process.env.DB_USER || 'app',
+  password: process.env.DB_PASSWORD || 'app123',
+});
+
+// GET /api/customers - Alle Kunden
+router.get('/', async (req, res) => {
+  try {
+    const { search, limit = 100 } = req.query;
+    
+    let query = `
+      SELECT k.*, 
+        (SELECT COUNT(*) FROM rechnungen WHERE kunde = k.name) as rechnungen_count,
+        (SELECT COALESCE(SUM(betrag), 0) FROM rechnungen WHERE kunde = k.name AND status = 'bezahlt') as total_umsatz
+      FROM kunden k
+    `;
+    const values = [];
+    
+    if (search) {
+      query += ` WHERE k.name ILIKE $1 OR k.email ILIKE $1 OR k.adresse ILIKE $1`;
+      values.push(`%${search}%`);
+    }
+    
+    query += ` ORDER BY k.name ASC LIMIT $${values.length + 1}`;
+    values.push(limit);
+    
+    const result = await pool.query(query, values);
+    
+    res.json({
+      success: true,
+      customers: result.rows.map(row => ({
+        ...row,
+        rechnungen_count: parseInt(row.rechnungen_count) || 0,
+        total_umsatz: parseFloat(row.total_umsatz) || 0
+      }))
+    });
+  } catch (error) {
+    console.error('Customers List Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// GET /api/customers/:id - Einzelner Kunde
+router.get('/:id', async (req, res) => {
+  try {
+    const { id } = req.params;
+    
+    // Kunde + Rechnungen
+    const [kundeResult, rechnungenResult] = await Promise.all([
+      pool.query('SELECT * FROM kunden WHERE id = $1', [id]),
+      pool.query(`
+        SELECT * FROM rechnungen 
+        WHERE kunde = (SELECT name FROM kunden WHERE id = $1)
+        ORDER BY datum DESC
+      `, [id])
+    ]);
+    
+    if (kundeResult.rows.length === 0) {
+      return res.status(404).json({ success: false, error: 'Kunde nicht gefunden' });
+    }
+    
+    const kunde = kundeResult.rows[0];
+    const rechnungen = rechnungenResult.rows;
+    
+    // Zusammenfassung
+    const totalUmsatz = rechnungen.reduce((sum, r) => sum + parseFloat(r.betrag || 0), 0);
+    const paidUmsatz = rechnungen
+      .filter(r => r.status === 'bezahlt')
+      .reduce((sum, r) => sum + parseFloat(r.betrag || 0), 0);
+    const openUmsatz = rechnungen
+      .filter(r => r.status === 'offen')
+      .reduce((sum, r) => sum + parseFloat(r.betrag || 0), 0);
+    
+    res.json({
+      success: true,
+      customer: {
+        ...kunde,
+        rechnungen,
+        summary: {
+          total_rechnungen: rechnungen.length,
+          total_umsatz: totalUmsatz,
+          paid_umsatz: paidUmsatz,
+          open_umsatz: openUmsatz
+        }
+      }
+    });
+  } catch (error) {
+    console.error('Customer Detail Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// POST /api/customers - Kunde erstellen
+router.post('/', async (req, res) => {
+  try {
+    const { name, adresse, plz, ort, email, telefon, notizen } = req.body;
+    
+    if (!name) {
+      return res.status(400).json({ success: false, error: 'Name ist erforderlich' });
+    }
+    
+    const query = `
+      INSERT INTO kunden (id, name, adresse, plz, ort, email, telefon, notizen, created_at, updated_at)
+      VALUES ($1, $2, $3, $4, $5, $6, $7, $8, NOW(), NOW())
+      RETURNING *
+    `;
+    const values = [uuidv4(), name, adresse || null, plz || null, ort || null, email || null, telefon || null, notizen || null];
+    
+    const result = await pool.query(query, values);
+    
+    res.status(201).json({
+      success: true,
+      customer: result.rows[0]
+    });
+  } catch (error) {
+    console.error('Customer Create Error:', error);
+    if (error.code === '23505') {
+      return res.status(409).json({ success: false, error: 'Kunde mit diesem Namen existiert bereits' });
+    }
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// PUT /api/customers/:id - Kunde aktualisieren
+router.put('/:id', async (req, res) => {
+  try {
+    const { id } = req.params;
+    const { name, adresse, plz, ort, email, telefon, notizen } = req.body;
+    
+    const query = `
+      UPDATE kunden 
+      SET 
+        name = COALESCE($1, name), 
+        adresse = COALESCE($2, adresse), 
+        plz = COALESCE($3, plz), 
+        ort = COALESCE($4, ort), 
+        email = COALESCE($5, email), 
+        telefon = COALESCE($6, telefon), 
+        notizen = COALESCE($7, notizen),
+        updated_at = NOW()
+      WHERE id = $8
+      RETURNING *
+    `;
+    const values = [name, adresse, plz, ort, email, telefon, notizen, id];
+    
+    const result = await pool.query(query, values);
+    
+    if (result.rows.length === 0) {
+      return res.status(404).json({ success: false, error: 'Kunde nicht gefunden' });
+    }
+    
+    res.json({
+      success: true,
+      customer: result.rows[0]
+    });
+  } catch (error) {
+    console.error('Customer Update Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// DELETE /api/customers/:id - Kunde löschen
+router.delete('/:id', async (req, res) => {
+  try {
+    const { id } = req.params;
+    
+    // Prüfe ob Kunde Rechnungen hat
+    const checkResult = await pool.query(`
+      SELECT COUNT(*) as count FROM rechnungen 
+      WHERE kunde = (SELECT name FROM kunden WHERE id = $1)
+    `, [id]);
+    
+    if (parseInt(checkResult.rows[0].count) > 0) {
+      return res.status(400).json({ 
+        success: false, 
+        error: 'Kunde kann nicht gelöscht werden - es existieren Rechnungen' 
+      });
+    }
+    
+    const result = await pool.query('DELETE FROM kunden WHERE id = $1 RETURNING *', [id]);
+    
+    if (result.rows.length === 0) {
+      return res.status(404).json({ success: false, error: 'Kunde nicht gefunden' });
+    }
+    
+    res.json({
+      success: true,
+      message: 'Kunde erfolgreich gelöscht',
+      deleted: result.rows[0]
+    });
+  } catch (error) {
+    console.error('Customer Delete Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+module.exports = router;
\ No newline at end of file
diff --git a/backend/routes/dashboard.js b/backend/routes/dashboard.js
new file mode 100644
index 0000000..bf7a1fd
--- /dev/null
+++ b/backend/routes/dashboard.js
@@ -0,0 +1,220 @@
+const express = require('express');
+const { Pool } = require('pg');
+
+const router = express.Router();
+
+// Database pool
+const pool = new Pool({
+  host: process.env.DB_HOST || 'db',
+  port: process.env.DB_PORT || 5432,
+  database: process.env.DB_NAME || 'steuer',
+  user: process.env.DB_USER || 'app',
+  password: process.env.DB_PASSWORD || 'app123',
+});
+
+// GET /api/dashboard/summary
+router.get('/summary', async (req, res) => {
+  try {
+    const currentYear = new Date().getFullYear();
+    
+    // Gesamtübersichten parallel abfragen
+    const [
+      rechnungenResult,
+      belegeResult,
+      krediteResult,
+      stundenResult,
+      kundenResult
+    ] = await Promise.all([
+      // Rechnungen dieses Jahr
+      pool.query(`
+        SELECT 
+          COUNT(*) as total_count,
+          COALESCE(SUM(CASE WHEN status = 'bezahlt' THEN betrag ELSE 0 END), 0) as paid_total,
+          COALESCE(SUM(CASE WHEN status = 'offen' THEN betrag ELSE 0 END), 0) as open_total,
+          COALESCE(SUM(betrag), 0) as total
+        FROM rechnungen 
+        WHERE EXTRACT(YEAR FROM datum) = $1
+      `, [currentYear]),
+      
+      // Belege/Ausgaben dieses Jahr
+      pool.query(`
+        SELECT 
+          COUNT(*) as total_count,
+          COALESCE(SUM(betrag), 0) as total
+        FROM belege 
+        WHERE EXTRACT(YEAR FROM date) = $1
+      `, [currentYear]),
+      
+      // Kredite
+      pool.query(`
+        SELECT 
+          COUNT(*) as total_count,
+          COUNT(CASE WHEN status = 'aktiv' THEN 1 END) as active_count,
+          COALESCE(SUM(CASE WHEN status = 'aktiv' THEN restschuld ELSE 0 END), 0) as total_restschuld,
+          COALESCE(SUM(CASE WHEN status = 'aktiv' THEN monatsrate ELSE 0 END), 0) as total_rate
+        FROM kredite
+      `),
+      
+      // Stunden dieses Jahr
+      pool.query(`
+        SELECT 
+          COUNT(*) as total_count,
+          COALESCE(SUM(stunden), 0) as total_stunden,
+          COALESCE(SUM(betrag), 0) as total_umsatz
+        FROM stunden 
+        WHERE EXTRACT(YEAR FROM datum) = $1
+      `, [currentYear]),
+      
+      // Kunden
+      pool.query(`
+        SELECT COUNT(*) as total_count FROM kunden
+      `)
+    ]);
+    
+    const rechnungen = rechnungenResult.rows[0];
+    const belege = belegeResult.rows[0];
+    const kredite = krediteResult.rows[0];
+    const stunden = stundenResult.rows[0];
+    const kunden = kundenResult.rows[0];
+    
+    res.json({
+      success: true,
+      year: currentYear,
+      summary: {
+        einnahmen: {
+          total: parseFloat(rechnungen.total) || 0,
+          paid: parseFloat(rechnungen.paid_total) || 0,
+          open: parseFloat(rechnungen.open_total) || 0,
+          count: parseInt(rechnungen.total_count) || 0
+        },
+        ausgaben: {
+          total: parseFloat(belege.total) || 0,
+          count: parseInt(belege.total_count) || 0
+        },
+        kredite: {
+          total: parseInt(kredite.total_count) || 0,
+          active: parseInt(kredite.active_count) || 0,
+          restschuld: parseFloat(kredite.total_restschuld) || 0,
+          monatsrate: parseFloat(kredite.total_rate) || 0
+        },
+        stunden: {
+          total: parseFloat(stunden.total_stunden) || 0,
+          umsatz: parseFloat(stunden.total_umsatz) || 0,
+          count: parseInt(stunden.total_count) || 0
+        },
+        kunden: {
+          total: parseInt(kunden.total_count) || 0
+        },
+        gewinn: (parseFloat(rechnungen.total) || 0) - (parseFloat(belege.total) || 0)
+      }
+    });
+  } catch (error) {
+    console.error('Dashboard Summary Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// GET /api/dashboard/cashflow
+router.get('/cashflow', async (req, res) => {
+  try {
+    const { months = 6 } = req.query;
+    
+    // Monatliche Cashflow-Daten
+    const cashflowData = [];
+    
+    for (let i = months - 1; i >= 0; i--) {
+      const date = new Date();
+      date.setMonth(date.getMonth() - i);
+      const year = date.getFullYear();
+      const month = date.getMonth() + 1;
+      
+      const [einnahmenResult, ausgabenResult] = await Promise.all([
+        pool.query(`
+          SELECT COALESCE(SUM(betrag), 0) as total 
+          FROM rechnungen 
+          WHERE EXTRACT(YEAR FROM datum) = $1 AND EXTRACT(MONTH FROM datum) = $2
+          AND status = 'bezahlt'
+        `, [year, month]),
+        pool.query(`
+          SELECT COALESCE(SUM(betrag), 0) as total 
+          FROM belege 
+          WHERE EXTRACT(YEAR FROM date) = $1 AND EXTRACT(MONTH FROM date) = $2
+        `, [year, month])
+      ]);
+      
+      const einnahmen = parseFloat(einnahmenResult.rows[0].total) || 0;
+      const ausgaben = parseFloat(ausgabenResult.rows[0].total) || 0;
+      
+      cashflowData.push({
+        year,
+        month,
+        monthName: date.toLocaleString('de-DE', { month: 'short' }),
+        einnahmen,
+        ausgaben,
+        saldo: einnahmen - ausgaben
+      });
+    }
+    
+    res.json({
+      success: true,
+      cashflow: cashflowData
+    });
+  } catch (error) {
+    console.error('Dashboard Cashflow Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// GET /api/dashboard/tax-preview
+router.get('/tax-preview', async (req, res) => {
+  try {
+    const { year = new Date().getFullYear() } = req.query;
+    
+    const [einnahmenResult, ausgabenResult, stundenResult] = await Promise.all([
+      pool.query(`
+        SELECT COALESCE(SUM(betrag), 0) as total 
+        FROM rechnungen 
+        WHERE EXTRACT(YEAR FROM datum) = $1 AND status = 'bezahlt'
+      `, [year]),
+      pool.query(`
+        SELECT COALESCE(SUM(betrag), 0) as total 
+        FROM belege 
+        WHERE EXTRACT(YEAR FROM date) = $1
+      `, [year]),
+      pool.query(`
+        SELECT COALESCE(SUM(betrag), 0) as total 
+        FROM stunden 
+        WHERE EXTRACT(YEAR FROM datum) = $1 AND status = 'bezahlt'
+      `, [year])
+    ]);
+    
+    const einnahmen = parseFloat(einnahmenResult.rows[0].total) || 0;
+    const ausgaben = parseFloat(ausgabenResult.rows[0].total) || 0;
+    const stundenEinnahmen = parseFloat(stundenResult.rows[0].total) || 0;
+    const gesamtEinnahmen = einnahmen + stundenEinnahmen;
+    const gewinn = gesamtEinnahmen - ausgaben;
+    
+    // Vereinfachte Steuerberechnung (nür Hinweis)
+    const estVorschuss = gewinn > 0 ? gewinn * 0.25 : 0; // ca. 25% ESt
+    
+    res.json({
+      success: true,
+      year: parseInt(year),
+      preview: {
+        einnahmen: {
+          rechnungen: einnahmen,
+          stunden: stundenEinnahmen,
+          gesamt: gesamtEinnahmen
+        },
+        ausgaben,
+        gewinn,
+        estVorschuss: Math.max(0, estVorschuss)
+      }
+    });
+  } catch (error) {
+    console.error('Dashboard Tax Preview Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+module.exports = router;
\ No newline at end of file
diff --git a/backend/routes/invoices.js b/backend/routes/invoices.js
new file mode 100644
index 0000000..8c12f30
--- /dev/null
+++ b/backend/routes/invoices.js
@@ -0,0 +1,314 @@
+const express = require('express');
+const { Pool } = require('pg');
+const { v4: uuidv4 } = require('uuid');
+
+const router = express.Router();
+
+// Database pool
+const pool = new Pool({
+  host: process.env.DB_HOST || 'db',
+  port: process.env.DB_PORT || 5432,
+  database: process.env.DB_NAME || 'steuer',
+  user: process.env.DB_USER || 'app',
+  password: process.env.DB_PASSWORD || 'app123',
+});
+
+// GET /api/invoices - Alle Rechnungen
+router.get('/', async (req, res) => {
+  try {
+    const { status, customer, year, limit = 100, offset = 0 } = req.query;
+    
+    let query = `
+      SELECT r.*, 
+        COALESCE(SUM(b.betrag), 0) as bezahlt
+      FROM rechnungen r
+      LEFT JOIN rechnung_zahlungen b ON r.id = b.rechnung_id
+      WHERE 1=1
+    `;
+    const values = [];
+    let paramCount = 0;
+    
+    if (status) {
+      paramCount++;
+      query += ` AND r.status = $${paramCount}`;
+      values.push(status);
+    }
+    
+    if (customer) {
+      paramCount++;
+      query += ` AND r.kunde ILIKE $${paramCount}`;
+      values.push(`%${customer}%`);
+    }
+    
+    if (year) {
+      paramCount++;
+      query += ` AND EXTRACT(YEAR FROM r.datum) = $${paramCount}`;
+      values.push(year);
+    }
+    
+    query += ` GROUP BY r.id ORDER BY r.datum DESC LIMIT $${++paramCount} OFFSET $${++paramCount}`;
+    values.push(limit, offset);
+    
+    const result = await pool.query(query, values);
+    
+    // Summen berechnen
+    const summaryQuery = `
+      SELECT 
+        COUNT(*) as total_count,
+        COALESCE(SUM(betrag), 0) as total_betrag,
+        COALESCE(SUM(CASE WHEN status = 'offen' THEN betrag ELSE 0 END), 0) as open_total,
+        COALESCE(SUM(CASE WHEN status = 'bezahlt' THEN betrag ELSE 0 END), 0) as paid_total
+      FROM rechnungen
+      WHERE 1=1
+      ${status ? ' AND status = $1' : ''}
+      ${year ? (status ? ' AND' : '') + ` EXTRACT(YEAR FROM datum) = $${status ? 2 : 1}` : ''}
+    `;
+    const summaryValues = [];
+    if (status) summaryValues.push(status);
+    if (year) summaryValues.push(year);
+    
+    const summaryResult = await pool.query(summaryQuery, summaryValues);
+    
+    res.json({
+      success: true,
+      invoices: result.rows.map(row => ({
+        ...row,
+        betrag: parseFloat(row.betrag) || 0,
+        ust_satz: parseFloat(row.ust_satz) || 19,
+        bezahlt: parseFloat(row.bezahlt) || 0,
+        offen: (parseFloat(row.betrag) || 0) - (parseFloat(row.bezahlt) || 0)
+      })),
+      summary: {
+        total_count: parseInt(summaryResult.rows[0].total_count) || 0,
+        total_betrag: parseFloat(summaryResult.rows[0].total_betrag) || 0,
+        open_total: parseFloat(summaryResult.rows[0].open_total) || 0,
+        paid_total: parseFloat(summaryResult.rows[0].paid_total) || 0
+      }
+    });
+  } catch (error) {
+    console.error('Invoices List Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// GET /api/invoices/:id - Einzelne Rechnung
+router.get('/:id', async (req, res) => {
+  try {
+    const { id } = req.params;
+    
+    const [rechnungResult, zahlungenResult] = await Promise.all([
+      pool.query('SELECT * FROM rechnungen WHERE id = $1', [id]),
+      pool.query(`
+        SELECT * FROM rechnung_zahlungen 
+        WHERE rechnung_id = $1 
+        ORDER BY datum DESC
+      `, [id])
+    ]);
+    
+    if (rechnungResult.rows.length === 0) {
+      return res.status(404).json({ success: false, error: 'Rechnung nicht gefunden' });
+    }
+    
+    const rechnung = rechnungResult.rows[0];
+    const zahlungen = zahlungenResult.rows;
+    const bezahlt = zahlungen.reduce((sum, z) => sum + parseFloat(z.betrag || 0), 0);
+    
+    res.json({
+      success: true,
+      invoice: {
+        ...rechnung,
+        betrag: parseFloat(rechnung.betrag) || 0,
+        ust_satz: parseFloat(rechnung.ust_satz) || 19,
+        zahlungen,
+        bezahlt,
+        offen: (parseFloat(rechnung.betrag) || 0) - bezahlt
+      }
+    });
+  } catch (error) {
+    console.error('Invoice Detail Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// POST /api/invoices - Rechnung erstellen
+router.post('/', async (req, res) => {
+  try {
+    const { 
+      kunde, 
+      kunde_email, 
+      kunde_adresse, 
+      leistung, 
+      betrag, 
+      ust_satz = 19, 
+      datum, 
+      faelligkeit,
+      rechnung_nr 
+    } = req.body;
+    
+    if (!kunde || !betrag) {
+      return res.status(400).json({ 
+        success: false, 
+        error: 'Kunde und Betrag sind erforderlich' 
+      });
+    }
+    
+    // Rechnungsnummer generieren falls nicht angegeben
+    let finalRechnungNr = rechnung_nr;
+    if (!finalRechnungNr) {
+      const countResult = await pool.query(`
+        SELECT COUNT(*) FROM rechnungen 
+        WHERE EXTRACT(YEAR FROM datum) = EXTRACT(YEAR FROM CURRENT_DATE)
+      `);
+      const count = parseInt(countResult.rows[0].count) + 1;
+      finalRechnungNr = `RE-${new Date().getFullYear()}-${String(count).padStart(3, '0')}`;
+    }
+    
+    const query = `
+      INSERT INTO rechnungen (
+        id, rechnung_nr, kunde, kunde_email, kunde_adresse, 
+        leistung, betrag, ust_satz, datum, faelligkeit, status, created_at
+      ) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, 'offen', NOW())
+      RETURNING *
+    `;
+    const values = [
+      uuidv4(),
+      finalRechnungNr,
+      kunde,
+      kunde_email || null,
+      kunde_adresse || null,
+      leistung || null,
+      betrag,
+      ust_satz,
+      datum || new Date(),
+      faelligkeit || null
+    ];
+    
+    const result = await pool.query(query, values);
+    
+    res.status(201).json({
+      success: true,
+      invoice: result.rows[0]
+    });
+  } catch (error) {
+    console.error('Invoice Create Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// PUT /api/invoices/:id - Rechnung aktualisieren
+router.put('/:id', async (req, res) => {
+  try {
+    const { id } = req.params;
+    const { 
+      kunde, kunde_email, kunde_adresse, leistung, 
+      betrag, ust_satz, datum, faelligkeit, status 
+    } = req.body;
+    
+    const query = `
+      UPDATE rechnungen 
+      SET 
+        kunde = COALESCE($1, kunde),
+        kunde_email = COALESCE($2, kunde_email),
+        kunde_adresse = COALESCE($3, kunde_adresse),
+        leistung = COALESCE($4, leistung),
+        betrag = COALESCE($5, betrag),
+        ust_satz = COALESCE($6, ust_satz),
+        datum = COALESCE($7, datum),
+        faelligkeit = COALESCE($8, faelligkeit),
+        status = COALESCE($9, status)
+      WHERE id = $10
+      RETURNING *
+    `;
+    const values = [
+      kunde, kunde_email, kunde_adresse, leistung,
+      betrag, ust_satz, datum, faelligkeit, status, id
+    ];
+    
+    const result = await pool.query(query, values);
+    
+    if (result.rows.length === 0) {
+      return res.status(404).json({ success: false, error: 'Rechnung nicht gefunden' });
+    }
+    
+    res.json({
+      success: true,
+      invoice: result.rows[0]
+    });
+  } catch (error) {
+    console.error('Invoice Update Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// DELETE /api/invoices/:id - Rechnung löschen
+router.delete('/:id', async (req, res) => {
+  try {
+    const { id } = req.params;
+    
+    // Lösche zuerst Zahlungen
+    await pool.query('DELETE FROM rechnung_zahlungen WHERE rechnung_id = $1', [id]);
+    
+    const result = await pool.query('DELETE FROM rechnungen WHERE id = $1 RETURNING *', [id]);
+    
+    if (result.rows.length === 0) {
+      return res.status(404).json({ success: false, error: 'Rechnung nicht gefunden' });
+    }
+    
+    res.json({
+      success: true,
+      message: 'Rechnung erfolgreich gelöscht',
+      deleted: result.rows[0]
+    });
+  } catch (error) {
+    console.error('Invoice Delete Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+// POST /api/invoices/:id/payment - Zahlung hinzufügen
+router.post('/:id/payment', async (req, res) => {
+  try {
+    const { id } = req.params;
+    const { betrag, datum, methode, notizen } = req.body;
+    
+    if (!betrag) {
+      return res.status(400).json({ success: false, error: 'Betrag ist erforderlich' });
+    }
+    
+    const query = `
+      INSERT INTO rechnung_zahlungen (id, rechnung_id, betrag, datum, methode, notizen, created_at)
+      VALUES ($1, $2, $3, $4, $5, $6, NOW())
+      RETURNING *
+    `;
+    const values = [uuidv4(), id, betrag, datum || new Date(), methode || 'Überweisung', notizen || null];
+    
+    const result = await pool.query(query, values);
+    
+    // Prüfe ob Rechnung nun vollständig bezahlt
+    const [rechnungResult, zahlungenSumResult] = await Promise.all([
+      pool.query('SELECT betrag FROM rechnungen WHERE id = $1', [id]),
+      pool.query('SELECT COALESCE(SUM(betrag), 0) as total FROM rechnung_zahlungen WHERE rechnung_id = $1', [id])
+    ]);
+    
+    const rechnungBetrag = parseFloat(rechnungResult.rows[0].betrag);
+    const bezahlt = parseFloat(zahlungenSumResult.rows[0].total);
+    
+    if (bezahlt >= rechnungBetrag) {
+      await pool.query(`UPDATE rechnungen SET status = 'bezahlt' WHERE id = $1`, [id]);
+    } else if (bezahlt > 0) {
+      await pool.query(`UPDATE rechnungen SET status = 'teilweise' WHERE id = $1`, [id]);
+    }
+    
+    res.json({
+      success: true,
+      payment: result.rows[0],
+      bezahlt,
+      offen: rechnungBetrag - bezahlt
+    });
+  } catch (error) {
+    console.error('Invoice Payment Error:', error);
+    res.status(500).json({ success: false, error: error.message });
+  }
+});
+
+module.exports = router;
\ No newline at end of file
diff --git a/backend/server.js b/backend/server.js
index cf53d25..9d19923 100644
--- a/backend/server.js
+++ b/backend/server.js
@@ -34,6 +34,15 @@ app.use('/uploads', express.static('uploads'));
 // Auth Routes
 app.use('/api/auth', authRoutes);
 
+// Neue API Routen (für Frontend)
+const dashboardRoutes = require('./routes/dashboard');
+const customersRoutes = require('./routes/customers');
+const invoicesRoutes = require('./routes/invoices');
+
+app.use('/api/dashboard', dashboardRoutes);
+app.use('/api/customers', customersRoutes);
+app.use('/api/invoices', invoicesRoutes);
+
 // Nebenkosten Routes laden
 const nebenkostenRoutes = require('./routes/nebenkosten');
 nebenkostenRoutes(app);