diff --git a/server.js b/server.js
index e2cd58a..18befa5 100644
--- a/server.js
+++ b/server.js
@@ -1171,55 +1171,28 @@ app.post('/api/invoices/:id/export', async (req, res) => {
             : 'https://sandbox-quickbooks.api.intuit.com';
 
 
-        // -------------------------------------------
-        // --- SCHRITT 3a: NÄCHSTE NUMMER ERMITTELN ---
-        console.log("🔍 Frage QBO nach der höchsten Rechnungsnummer...");
+        // --- SCHRITT 3a: NÄCHSTE NUMMER ERMITTELN (lokal) ---
+        // Wir nehmen das Maximum aus qbo_doc_number UND invoice_number
+        const maxNumResult = await client.query(`
+            SELECT GREATEST(
+                COALESCE((SELECT MAX(CAST(qbo_doc_number AS INTEGER)) FROM invoices WHERE qbo_doc_number ~ '^[0-9]+$'), 0),
+                COALESCE((SELECT MAX(CAST(invoice_number AS INTEGER)) FROM invoices WHERE invoice_number ~ '^[0-9]+$'), 0)
+            ) as max_num
+        `);
+        let nextDocNumber = (parseInt(maxNumResult.rows[0].max_num) + 1).toString();
+        console.log(`✅ Nächste Nummer (aus lokaler DB): ${nextDocNumber}`);
 
-        // Alle Rechnungen laden (nur DocNumber Feld), nach DocNumber absteigend
-        // QBO unterstützt leider kein MAX() oder CAST, daher holen wir die letzten 100
-        // und ermitteln die höchste rein numerische Nummer clientseitig.
-        const numQuery = "SELECT DocNumber FROM Invoice ORDERBY DocNumber DESC MAXRESULTS 100";
-        const lastNumResponse = await makeQboApiCall({
-            url: `${baseUrl}/v3/company/${companyId}/query?query=${encodeURI(numQuery)}`,
-            method: 'GET'
-        });
-
-        const lastNumData = lastNumResponse.getJson ? lastNumResponse.getJson() : lastNumResponse.json;
-        let nextDocNumber = null;
-
-        if (lastNumData.QueryResponse?.Invoice?.length > 0) {
-            // Nur rein numerische DocNumbers betrachten (keine "110444-A" etc.)
-            const numericDocs = lastNumData.QueryResponse.Invoice
-                .map(inv => inv.DocNumber)
-                .filter(dn => /^\d+$/.test(dn))
-                .map(dn => parseInt(dn, 10))
-                .sort((a, b) => b - a); // Absteigend
-
-            if (numericDocs.length > 0) {
-                const highest = numericDocs[0];
-                nextDocNumber = (highest + 1).toString();
-                console.log(`✅ Höchste numerische Nummer: ${highest}. Neue Nummer: ${nextDocNumber}`);
-            }
-        }
-
-        // Fallback
-        if (!nextDocNumber) {
-            console.log("⚠️ Konnte keine Nummer aus QBO ermitteln. Verwende lokale Nummer.");
-            nextDocNumber = invoice.invoice_number;
-        }
-        
         // 4. QBO JSON bauen
         const lineItems = items.map(item => {
             const rate = parseFloat(item.rate.replace(/[^0-9.]/g, '')) || 0;
             const amount = parseFloat(item.amount.replace(/[^0-9.]/g, '')) || 0;
-            
-            const itemRefId = item.qbo_item_id || QBO_PARTS_ID; 
+            const itemRefId = item.qbo_item_id || QBO_PARTS_ID;
             const itemRefName = itemRefId == QBO_LABOR_ID ? "Labor:Labor" : "Parts:Parts";
 
             return {
                 "DetailType": "SalesItemLineDetail",
                 "Amount": amount,
-                "Description": item.description, 
+                "Description": item.description,
                 "SalesItemLineDetail": {
                     "ItemRef": { "value": itemRefId, "name": itemRefName },
                     "UnitPrice": rate,
@@ -1230,49 +1203,62 @@ app.post('/api/invoices/:id/export', async (req, res) => {
 
         const qboInvoicePayload = {
             "CustomerRef": { "value": invoice.customer_qbo_id },
-            
-            // HIER SETZEN WIR DIE ERMITTELTE NUMMER EIN
             "DocNumber": nextDocNumber,
-            
             "TxnDate": invoice.invoice_date.toISOString().split('T')[0],
             "Line": lineItems,
             "CustomerMemo": { "value": invoice.auth_code ? `Auth: ${invoice.auth_code}` : "" },
-            
-            // Status auf "Verschickt" setzen
             "EmailStatus": "EmailSent",
             "BillEmail": { "Address": invoice.email || "" }
         };
 
-        console.log(`📤 Sende Rechnung an QBO (DocNumber: ${nextDocNumber})...`);
-        
-        const createResponse = await makeQboApiCall({
-            url: `${baseUrl}/v3/company/${companyId}/invoice`,
-            method: 'POST',
-            headers: { 'Content-Type': 'application/json' },
-            body: JSON.stringify(qboInvoicePayload)
-        });
+        // 5. An QBO senden — mit Retry bei Duplicate
+        let qboInvoice = null;
+        const MAX_RETRIES = 5;
 
-        const responseData = createResponse.getJson ? createResponse.getJson() : createResponse.json;
-        // Check auf Unterobjekt "Invoice"
-        const qboInvoice = responseData.Invoice || responseData;
+        for (let attempt = 0; attempt < MAX_RETRIES; attempt++) {
+            console.log(`📤 Sende Rechnung an QBO (DocNumber: ${qboInvoicePayload.DocNumber})...`);
 
-        console.log("🔍 FULL QBO RESPONSE (ID):", qboInvoice.Id);
+            const createResponse = await makeQboApiCall({
+                url: `${baseUrl}/v3/company/${companyId}/invoice`,
+                method: 'POST',
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify(qboInvoicePayload)
+            });
 
-        if (!qboInvoice.Id) {
-            console.error("FULL RESPONSE DUMP:", JSON.stringify(responseData, null, 2));
-            throw new Error("QBO hat keine ID zurückgegeben.");
+            const responseData = createResponse.getJson ? createResponse.getJson() : createResponse.json;
+
+            // Prüfe auf Duplicate Error (code 6140)
+            if (responseData.Fault?.Error?.[0]?.code === '6140') {
+                const oldNum = parseInt(qboInvoicePayload.DocNumber);
+                qboInvoicePayload.DocNumber = (oldNum + 1).toString();
+                console.log(`⚠️ DocNumber ${oldNum} existiert bereits. Versuche ${qboInvoicePayload.DocNumber}...`);
+                continue;
+            }
+
+            qboInvoice = responseData.Invoice || responseData;
+
+            if (qboInvoice.Id) {
+                break; // Erfolg!
+            } else {
+                console.error("FULL RESPONSE DUMP:", JSON.stringify(responseData, null, 2));
+                throw new Error("QBO hat keine ID zurückgegeben: " +
+                    (responseData.Fault?.Error?.[0]?.Message || JSON.stringify(responseData)));
+            }
+        }
+
+        if (!qboInvoice || !qboInvoice.Id) {
+            throw new Error(`Konnte nach ${MAX_RETRIES} Versuchen keine freie DocNumber finden.`);
         }
 
         console.log(`✅ QBO Rechnung erstellt! ID: ${qboInvoice.Id}, DocNumber: ${qboInvoice.DocNumber}`);
 
-        // 6. DB Update: Wir speichern AUCH die QBO-Nummer, damit wir wissen, wie sie drüben heißt
+        // 6. DB Update
         await client.query(
-            `UPDATE invoices SET qbo_id = $1, qbo_sync_token = $2, qbo_doc_number = $3, invoice_number = $3 WHERE id = $4`,
-            [qboInvoice.Id, qboInvoice.SyncToken, qboInvoice.DocNumber, id]
+            `UPDATE invoices SET qbo_id = $1, qbo_sync_token = $2, qbo_doc_number = $3, invoice_number = $4 WHERE id = $5`,
+            [qboInvoice.Id, qboInvoice.SyncToken, qboInvoice.DocNumber, qboInvoice.DocNumber, id]
         );
 
-        // Wir geben die neue Nummer zurück, damit das Frontend Bescheid weiß
-        res.json({ success: true, qbo_id: qboInvoice.Id, qbo_doc_number: qboInvoice.DocNumber });
+        res.json({ success: true, qbo_id: qboInvoice.Id, qbo_doc_number: qboInvoice.DocNumber });            
 
     } catch (error) {
         console.error("QBO Export Error:", error);