woocommerce_before_thankyou” is a hook used to add content or process before the order details in Woocommerce Order Received Page

Sample Code:

Note: This sample code is for creating invoice with WPCargo Advance Invoice upon successful checkout.

<?php
/************************************************
 * Custom Create Invoice on Successful Checkout
 ***********************************************/
function create_custom_invoice_on_checkout( $order_id ) {
    if ( ! $order_id ){
        return;
    }
    $order = wc_get_order( $order_id );
    $order_shipments = array();

    /***********************************************
     * Get assigned shipment from order received
    ***********************************************/
    foreach ( $order->get_items() as $item_id => $item ) {
        $meta_value = $item->get_meta( 'Saadetise', true );
        $shipment_id = get_page_by_title( $meta_value, OBJECT, 'wpcargo_shipment')->ID;
        array_push( $order_shipments , $shipment_id );

        $rate_id    = get_post_meta( $shipment_id, 'shipment_rate', true );
        $rateInfo 	= get_wpcsr_rate_by_id( $rate_id );
    }

    $assigned_shipments = implode( ',', $order_shipments);
    $status         = '';

    if( $order->get_payment_method() != 'cod' ){
        $status     = 'wpci-paid';
    }else{
        $status     = 'wpci-unpaid';
    }
    
    $invoice_id         = (int)$_POST['invoice_id'];
    $process_type       = 'update';
    $invoice_number = wpcadvinv_generated_invoice_number();

    /*************************************************
     * SAVE INVOICE POICE TYPE AS ADVANCE INVOICE
     ************************************************/
    if( !$invoice_id ){
        $invoice_args = array(
            'post_title'    => $invoice_number,
            'post_status'   => 'publish',
            'post_type'     => WPC_ADVANCE_INVOICE_POSTTYPE
        );
        // Insert the post into the database
        $invoice_id         = wp_insert_post( $invoice_args );
        $process_type       = 'add';
    }

    if ( is_wp_error( $invoice_id ) ) {
        echo '<div id="message" class="error"><p>' . $invoice_id->get_error_message() . '</p></div>';
        wp_die();
    }

    /**********************************************************
     * Assign shipment to invoice
    **********************************************************/
    $old_post_meta      = null;
    $invoice_history    = array();
    if( $process_type == 'update' ){
        $old_post_meta      = get_post_meta( $invoice_id );
        $invoice_history    = $old_post_meta['_invoice_history'];
        unset( $old_post_meta['_invoice_history'] ); // Remove the Invoice history
    }
    
    update_post_meta( $invoice_id, '_invoice_status', $status );
    update_post_meta( $invoice_id, '_wpcadvinv_assigned_shipments', $assigned_shipments );

    $assigned_shipments = $assigned_shipments ? explode(',', $assigned_shipments ) : array(); 
    foreach ( $assigned_shipments as $shipment_id ) {
        if( !(int)$shipment_id ){
            continue;
        }
        update_post_meta( (int)$shipment_id, '_advance_invoice', $invoice_id );
    }

    /**********************************************************
     * Save billing fields for the advanced invoice
    *********************************************************/
    $order_data = $order->get_data();

    $user_data  = get_userdata( $user_id );
    $first_name = $order_data['billing']['first_name'];
    $last_name  = $order_data['billing']['last_name'];
    $company    = $order_data['billing']['company'];
    $address_1  = $order_data['billing']['address_1'];
    $city       = $order_data['billing']['city'];
    $postcode   = $order_data['billing']['postcode'];
    $email      = $order_data['billing']['email'];
    $phone      = $order_data['billing']['phone'];

    update_post_meta( $invoice_id, '_business_name', $company );
    update_post_meta( $invoice_id, '_business_phone', $phone );
    update_post_meta( $invoice_id, '_business_email', $email );
    update_post_meta( $invoice_id, '_business_address', $address_1 );
    update_post_meta( $invoice_id, '_business_city', $city );
    update_post_meta( $invoice_id, '_business_zipcode', $postcode );

    /******************************************
     * Send Invoice Email Notification
     * ****************************************/

    if( $email != '' ){
        wpcadvinv_invoice_send_mail( $invoice_id );
    }

    /********************************************
     * Update Invoice History
     *******************************************/
    do_action( 'wpcadv_invoice_after_data_save', $invoice_id );
    $new_history        = array(
        'date'       => current_time( $wpcargo->date_format ),
        'time'       => current_time( $wpcargo->time_format ),
        'old_data'   => $old_post_meta,
        'new_data'   => get_post_meta( $invoice_id ),
        'updated_by' => wp_get_current_user()->display_name,
        'type'       => $process_type
    );
    // Invoice History
    $invoice_history[]  = $new_history;
    add_post_meta( $invoice_id, '_invoice_history', $invoice_history );
    do_action( 'wpcadv_invoice_after_data_history_save', $invoice_id );

    
    /********************************************
     * Download invoice functionality
     *******************************************/
     $invoice_data = wpccustom_generate_invoice_pdf( $invoice_id );
    ?>

    <div class="text-center print-shipment">
       <a class="btn btn-primary" href = "<?php echo $invoice_data['file_url']; ?>" download > Download Invoice </a>
    </div>

    <?php
}

add_action('woocommerce_before_thankyou', 'create_custom_invoice_on_checkout', 10, 1);