diff --git a/server.js b/server.js
index 56d59f0..ebe4ff9 100644
--- a/server.js
+++ b/server.js
@@ -194,12 +194,18 @@ async function exportInvoiceToQbo(invoiceId, client) {
         const data = response.getJson ? response.getJson() : response.json;
 
         if (data.Fault?.Error?.[0]?.code === '6140') {
+            console.log(`   ⚠️ DocNumber ${qboPayload.DocNumber} exists, retrying...`);
             qboPayload.DocNumber = (parseInt(qboPayload.DocNumber) + 1).toString();
             continue;
         }
+        if (data.Fault) {
+            const errMsg = data.Fault.Error?.map(e => `${e.code}: ${e.Message} - ${e.Detail}`).join('; ') || JSON.stringify(data.Fault);
+            console.error(`❌ QBO Export Fault:`, errMsg);
+            throw new Error('QBO export failed: ' + errMsg);
+        }
         qboInvoice = data.Invoice || data;
         if (qboInvoice.Id) break;
-        throw new Error("QBO returned no ID: " + (data.Fault?.Error?.[0]?.Message || JSON.stringify(data)));
+        throw new Error("QBO returned no ID: " + JSON.stringify(data).substring(0, 500));
     }
 
     if (!qboInvoice?.Id) throw new Error('Could not find free DocNumber after 5 attempts.');
@@ -279,8 +285,19 @@ async function syncInvoiceToQbo(invoiceId, client) {
     });
 
     const updateData = updateRes.getJson ? updateRes.getJson() : updateRes.json;
+
+    // Prüfe auf Fault
+    if (updateData.Fault) {
+        const errMsg = updateData.Fault.Error?.map(e => `${e.code}: ${e.Message} - ${e.Detail}`).join('; ') || JSON.stringify(updateData.Fault);
+        console.error(`❌ QBO Sync Fault:`, errMsg);
+        throw new Error('QBO sync failed: ' + errMsg);
+    }
+
     const updated = updateData.Invoice || updateData;
-    if (!updated.Id) throw new Error('QBO update returned no ID');
+    if (!updated.Id) {
+        console.error(`❌ QBO unexpected response:`, JSON.stringify(updateData).substring(0, 500));
+        throw new Error('QBO update returned no ID');
+    }
 
     await client.query(
         'UPDATE invoices SET qbo_sync_token = $1, updated_at = CURRENT_TIMESTAMP WHERE id = $2',