Developers can extend the checkout and order lifecycle with WordPress actions and filters. Two of the most useful are shown below.

Use the revcommerce_order_complete action to run custom logic when an order is paid, fulfilling a license, syncing to a CRM, or notifying a fulfillment service:

add_action( 'revcommerce_order_complete', function( $order_id, $order ) {
    foreach ( $order->get_items() as $item ) {
        if ( 'license' === $item['type'] ) {
            my_issue_license( $order->get_email(), $item );
        }
    }
    my_crm_sync_order( $order );
}, 10, 2 );

Use the revcommerce_cart_item_price filter to adjust a line price before totals are calculated, here we apply a member discount:

add_filter( 'revcommerce_cart_item_price', function( $price, $item, $cart ) {
    if ( is_user_logged_in() && current_user_can( 'member' ) ) {
        $price = round( $price * 0.9, 2 );
    }
    return $price;
}, 10, 3 );

Other commonly used hooks include revcommerce_order_status_changed, revcommerce_payment_complete, revcommerce_email_recipients, and revcommerce_download_url (sign or rewrite a download link). See the full reference in the developer docs.