Prevent Discounts on Renewals

function kfg_check_if_is_renewal( $return, $discount_id ) {

    // Check if the discount code is valid and is not for renewals.

    if ( EDD()->session->get( 'edd_is_renewal' ) ) {

        edd_set_error( 'edd-discount-error', __( 'This discount is not valid with renewals.', 'edd' ) );

        return false;

    }

    return $return;

}

add_filter( 'edd_is_discount_valid', 'kfg_check_if_is_renewal', 99, 2 );