Split orders when order containing products from multiple vendor is created from admin dashboard in Dokan plugin.

dokan-order-split-from-backend.php

<?php
/**
 * Split orders when order containing products from multiple vendor is created from admin dashboard.
 */
function sagar_order_creation_fix( $post_id, $post, $update ) {
    // Bail early if not admin.
    if( ! is_admin() ) {
        return;
    }

    // Split the order if the order is created.
    if ( 'draft' === get_post_status( $post_id ) ) {
        remove_action( 'save_post_shop_order', 'sagar_order_creation_fix', 10 );

        $order_manager = new Dokan_Order_Manager();
        $order_manager->maybe_split_orders( $post_id );

        add_action( 'save_post_shop_order', 'sagar_order_creation_fix', 10, 3 );
    }

}
add_action( 'save_post_shop_order', 'sagar_order_creation_fix', 10, 3 );