debug: log raw e-taxes payload to Error Log before sending

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

invoice_az/send_sales_api.py

@@ -566,6 +566,11 @@ def create_invoice_on_etaxes(token, payload, serial_number):
         headers = DEFAULT_HEADERS.copy()
         headers["x-authorization"] = f"Bearer {token}"
 
+        frappe.log_error(
+            json.dumps(payload, indent=2, ensure_ascii=False),
+            "E-Taxes Send Payload DEBUG"
+        )
+
         response = requests.post(
             INVOICE_URL,
             data=json.dumps(payload),