Okay, I'm giving you the solution.

[php]
function wpufe_render_bus_tags( $form_id, $post_id, $form_settings ) {
$value = ”;

if ( $post_id ) {
$post_tags = wp_get_post_terms( $post_id, ‘business_tags' );
$tagsarray = array();
foreach ($post_tags as $tag) {
$tagsarray[] = $tag->name;
}

$value = implode( ‘, ‘, $tagsarray );
}
?>
<div class="wpuf-label">Business Tags</div>
<div class="wpuf-fields">
<input type="text" name="business_tags" value="<?php echo esc_attr( $value ); ?>" size="40">
</div>
<?php
}

add_action( ‘wpufe_bus_tags', ‘wpufe_render_bus_tags', 10, 3 );

function wpufe_inesrt_business_tags( $post_id ) {
if ( isset( $_POST[‘business_tags'] ) ) {
$tags = explode( ‘,', $_POST[‘business_tags'] );
wp_set_post_terms( $post_id, $tags, ‘business_tags' );
}
}

add_action( ‘wpuf_add_post_after_insert', ‘wpufe_inesrt_business_tags' );
add_action( ‘wpuf_edit_post_after_update', ‘wpufe_inesrt_business_tags' );
[/php]

This code adds a input field named Business Tags. You've to create a action hook field and give the label wpufe_bus_tags and paste this code to your themes functions.php. Now you'll see a input field just like tags and you can input your business_tags taxonomy.

This solution works great. How can I make the custom taxonomy form field required?

I'm using this action hook to allow users to add “custom” taxonomy tags such as genre, artist, year, etc. The hook works perfectly. I just want to know how I can make the form field a required value.

Hey Tareg,
it also works for me, BUT: when I fill in the custom taxonomy tags in the WP backend, I get suggestions of already existing tags. For example I'm using a custom taxonomy “filmmaker”. If I type the first letters “St”, it shows me the tags, that already exist e.g. “Steven Spielberg”. However this doesn't seem to be working in the front end form. Is there a way to make this work? That'd be fantastic! 🙂

Thanks Tareq for your super fast answer!