Payment method not working

I am using 1stpaygateway plugin https://www.ads-software.com/plugins/1stpaygateway-for-woocommerce/#description and filled payment gateway credentials in the backend provided by the support. Here is a backend screenshot https://prnt.sc/5Hho_PO8JQND.

Here is the website I am using the plugin https://distinctlyhimalayan.com/checkout/ and when I tried to pay I got https://prnt.sc/tK1Ck7lZtCql error. I am using test payment details mention here https://support.1stpaygateway.net/transaction-center.aspx?article=test-credit-card-numbers and here is screenshot of card details https://prnt.sc/jFiJI1pfmDOJ

Please Guide me ASAP.

The page I need help with: [log in to see the link]