There are two ways for an order to be confirmed in the store, either via a callback from Vipps (which is what your log indicates was successful) and via polling from the store (which has to be implemented because the callback is not guaranteed, and which fails in your case).
When returning from Vipps, the order id is not passed, so to find out what order we are waiting for the status on, we use the Woocommerce session to store the ‘currently pending order’ . In your case, this seems to be empty. The code that causes the error message is this in vipps_wait_for_payment:
$orderid = WC()->session->get('_vipps_pending_order');
$order = null;
if ($orderid) {
$order = new WC_Order($orderid);
}
if (!$order) wp_die(__('Unknown order', 'woo-vipps'));
Do you have any plugins that could conceivably modify how Woo’s sessions work, or something that would block your cookies on return to the sites? (This could be done by front-end caching systems like Varnish as well). Otherwise, there should really be an active Woo-session with your order id stored.
Unfortunately, in this case no information is passed from Vipps to the store as to which order we are waiting for, so there is no easy way to fail more softly here.
