Yes we are using storefront theme
Here is our log, we have tried 2 clean test-environments with only WooCommerce and your plugin installed and activated, with everything latest version. We have set checkout page. Here is our log
12-01-2020 @ 10:00:33 – Order shipping does not match.
12-01-2020 @ 10:00:33 – Received error when create Svea order: Undefined error occurred.
12-01-2020 @ 10:01:00 – Order shipping does not match.
12-01-2020 @ 10:01:01 – Received error when create Svea order: Undefined error occurred.
12-01-2020 @ 10:01:13 – Order cart hash does not match.
12-01-2020 @ 10:01:13 – Received error when create Svea order: Undefined error occurred.
12-01-2020 @ 10:01:33 – Order cart hash does not match.
12-01-2020 @ 10:01:33 – Received error when create Svea order: Undefined error occurred.
12-01-2020 @ 10:02:11 – Received error when create Svea order: Undefined error occurred.
12-01-2020 @ 10:03:01 – Received error when create Svea order: Undefined error occurred.
12-01-2020 @ 10:03:04 – Received error when create Svea order: Undefined error occurred.
