[FIX] datev_export_xml: Add general check on invoice e.g. when multip…

…le taxes exists

datev_export_xml/models/datev_export.py

@@ -357,6 +357,12 @@ def _create_activity(self):
     def action_validate(self):
         generator = self.env["datev.xml.generator"]
         for invoice in self.invoice_ids:
+            try:
+                generator._check_invoices(invoice)
+            except ValueError as e:
+                invoice.datev_validation = str(e)
+                continue
+
             try:
                 generator.generate_xml_invoice(invoice)
             except UserError: