More than one checkout processes?

You programmatically modify the steps on one checkout page and not on the other.

For example, if you create two checkout pages, one with page ID 100 and the second one with page ID 101, then the following PHP snippet will add the “Cross-sales” custom step only to the checkout page with ID 100:

if ( ! function_exists( 'wpmc_add_cross_sales_step' ) ) {
    function wpmc_add_cross_sales_step( $steps ) {
        global $post;
        if ( $post->ID == 100 ) {
            $steps['cross_sales'] = array(
              'title'     => __( 'Cross-Sales' ),
              'position'  => 25,
              'class'     => 'wpmc-step-cross-sales',
              'sections'  => array( 'cross_sales' ),
            );  
        }
        return $steps;
    }
}
add_filter( 'wpmc_modify_steps', 'wpmc_add_cross_sales_step' );

The PHP snippet will work both with the free and the pro version of the plugin.