Just say Error, since we show this error for all errors, not just transaction errors

src/connection.cpp

@@ -958,7 +958,7 @@ void Connection::showTxError(const QString& error) {
         return;
 
     shown = true;
-    QMessageBox::critical(main, QObject::tr("Transaction Error"), QObject::tr("There was an error! : ") + "\n\n"
+    QMessageBox::critical(main, QObject::tr("Error"), QObject::tr("There was an error! : ") + "\n\n"
         + error, QMessageBox::StandardButton::Ok);
     shown = false;
 }