open the Checkout page for editing in the admin, select the Checkout widget on the page and set the “Skin” option to “Multi-Step Checkout” in the widget’s options? Reload the checkout page on the frontend to see if the Payment section shows up alright. If that doesn’t work, then
would you check if this is an incompatibility issue with the GreenMart theme? Change the theme on your staging website to a default one (for example, Twentytwentyfour) and see if the payment gateway still shows up twice.