Thank you for your quick reply.
I enabled the Express Checkout payment option by checking the box for the "Enable/Disable" field on the settings, located at the top of the page (first field listed).
I also checked the box for the "Standard Checkout" field to "Show Express Checkout button on checkout page", located lower on the same settings page.
Yet, still having the same issue: no payment option on the Checkout page. Only on the View Cart one :(