John Davidson

Message:

$post_type = 'machine';

$title     = $_POST['name'];

$new_post = array(

'post_title'    => $title,

'post_status'   => 'publish',          

'post_type'     => $post_type,

);

$pid = wp_insert_post($new_post);

$category_id = trim($_POST['category']);

$taxonomy = 'machine_categories';

wp_set_object_terms( $pid, (int)$category_id, $taxonomy, true );

Here i create a new post type machine and new taxonomy machine_categories
A new custom form created in the front end

<div class="form-group">

    <input type="text" class="form-input" name="name" id="name" placeholder="Post Title" />

</div>

<div class="form-group">

    <label>Post Category</label>

    <select class="form-input" name="category" id="category">

        <option>--Select--</option>

        <?php 

        $terms=g et_terms( array( 'taxonomy'=>'machine_categories', 'hide_empty' => false, ) ); 

        if ( ! empty( $terms ) && is_array( $terms ) ) 

            { 

                foreach ( $terms as $term ) {

        ?>

        <option value="<?php echo $term->term_id; ?>"><?php echo $term->name; ?></option>

        <?php 

            } 

        } 

        ?>

    </select>

</div>

Here is the dropdown code in the frontend, when i submit the post there is an error shows Invalid Taxonomy
This taxonomy and post type created using Custom post type ui plugin.

---

My Answer:
$title,
'post_type' => $post_type,
'post_status' => 'publish'
);

$post_id = wp_insert_post($new_post);

$taxonomy = 'machine_category';
$terms = array('category1', 'category2');

wp_set_object_terms($post_id, $terms, $taxonomy);