Preface: IANAFED (front-end developer).

When rendering a field inside of an already existing meta box, it does not expand the meta box to include it.

HTML below:

<div id="project-details" class="postbox " >
    <button type="button" class="handlediv button-link" aria-expanded="true"><span class="screen-reader-text">Toggle panel: Project Details</span><span class="toggle-indicator" aria-hidden="true"></span></button><h2 class='hndle'><span>Project Details</span></h2>
    <div class="inside">
        <p>
            <label for="featured_project">Featured project</label>
            <input type="checkbox" id="featured_project" name="featured_project" value="1" class="widefat">
        </p><div class=" piklist-field-container"><div class="piklist-field-container-row"><div class="piklist-label-container"><label for="_post_meta[gallery_images][]" class="piklist-field-part piklist-label piklist-label-position-before " >Gallery images</label><p class="piklist-field-description description">Select/Upload images to use on the single project page</p></div><div class="piklist-field"><div class="piklist-field-part">

        <a
                href="#"
                class="button piklist-upload-file-button piklist-field-part "
                title="Select Images"
        >
            Select Images    </a>

        <div class="piklist-upload-file-preview piklist-field-preview">
            

        </div>

    </div></div></div></div></div>
</div>
</div>

The code used to render the field is as follows:

/**
     * @param string $id
     * @param array  $params
     */
    function _gallery_input( $id, $params ) {

        $params = wp_parse_args( $params, [
            'label' => 'Please enter a label for this field',
            'modal_title' => 'Select Images',
            'button_text' => 'Select Images',
        ] );

        piklist('field', array(
            'type' => 'file',
            'field' => $id,
            'label' => $params['label'],
            'description' => __( 'Select/Upload images to use on the single project page', 'rcg' ),
            'options' => array(
                'modal_title' => $params['modal_title'],
                'button' => $params['button_text'],
                'multiple' => true,
            ),
        ));

    }

Any help would be greatly appreciated.