Metabox function for repeat_metabox.php

meta-slider.php

<?php

function iv_slider_metabox( array $meta_boxes ) {

    $fields = array(
        array( 'id' => 'iv-slider-title',  'name' => 'Text input field', 'type' => 'text' ),
        array( 'id' => 'iv-slider-desc',  'name' => 'WYSIWYG field', 'type' => 'wysiwyg', 'options' => array( 'editor_height' => '100' ) ),
        array( 'id' => 'iv-slider-img', 'name' => 'File field', 'type' => 'file', 'file_type' => 'image', 'repeatable' => 1, 'sortable' => 1 ),
    );

    /* YOU WILL NEED TO ADD THIS */
    $group_fields = $fields;
    foreach ( $group_fields as &$field ) {
        $field['id'] = str_replace( 'field', 'gfield', $field['id'] );
    }

    $meta_boxes[] = array(
        'title' => 'Image Slider',
        'pages' => 'page',
        'fields' => array(
            array( 
                'id' => 'gp', 
                'name' => 'Individual slide options', 
                'type' => 'group', 
                'repeatable' => true,
                'sortable' => true,
                'fields' => $group_fields
            )
        )
    );

    return $meta_boxes;

}

add_filter( 'cmb_meta_boxes', 'iv_slider_metabox' );

?>