Notice: Undefined index: shoppingcartid when activating the plugin, and checkout not working

[davorin1]

Describe the bug
After activating T-Com PayWay (new release) I am getting this error: Undefined index: shoppingcartid in /home/mydomain/public_html/wp-content/plugins/woocommerce-tcom-payway-1.7.3/classes/class-wc-tpayway.php on line 487

When going to the Checkout page, the payment is either in infinite loop or after trying to checkout with the PayWay as a payment type, the page just refreshes, order is pending and nothing else happens.

On previous versions this was working.

I guess it may be related to the WooCommerce version also, because the same plugin was working on much older WP/WooCommerce version.

To Reproduce

Version
1.7.3

Expected behavior
The Checkout page redirects to PayWay (like it used to) and after successful payment redirects to thank you page.

Additional context