Hi,
I4ve checked the code of the plugin and as it was developed by a sub contractor, they didn't use the standard way we do in other payment plugins to send the taxes.
Try changing the code:
if(isset($product->order_product_tax_info[0]->tax_rate) && $product->order_product_tax_info[0]->tax_rate > 0) {
$product_tax = 100 * ($product->order_product_tax_info[0]->tax_rate);
}
to:
if(isset($product->order_product_tax) && $product->order_product_tax > 0) {
$product_tax = 100 * $product->order_product_tax;
}
in the file plugins/hikashoppayment/sveawebpay/sveawebpay.php
That should hopefully solve the problem.
Let us know how it goes so that we can include the patch for the next version.