If looks like you are using CMB (Custom-Metaboxes-and-Fields-for-WordPress) to create your create metaboxes.
CMB is already supplying a option to group and repeat meta box that you can use. You can check this link
As far as your code it is concern if suppose it should go like this:
function dikka_cmb_meoxes( array $meta_boxes ) {
$prefix = 'dikka_';
$meta_boxes['details_meox'] = array(
'id' => $prefix . 'details_meox',
'type' => 'group',
'pages' => array( 'portfolio', ), // Post type
'description' => __( 'Porject Details', 'dikka' ),
'options' => array(
'group_title' => __( 'Entry {#}', 'dikka' ), // since version 1.1.4, {#} gets replaced by row number
'add_button' => __( 'Add Another Entry', 'dikka' ),
'remove_button' => __( 'Remove Entry', 'dikka' ),
'sortable' => true, // beta
),
// Fields array works the same, except id's only need to be unique for this group. Prefix is not needed.
'fields' => array(
array(
'name' => __( 'Client', 'dikka' ),
'desc' => __( 'Add client name', 'dikka' ),
'id' => $prefix . 'add_client',
'type' => 'text',
),
array(
'name' => __( 'Skills', 'dikka' ),
'desc' => __( 'Add skills', 'dikka' ),
'id' => $prefix . 'skills',
'type' => 'text',
),
array(
'name' => __( 'Release Date', 'dikka' ),
'desc' => __( 'Add release date of project', 'dikka' ),
'id' => $prefix . 'add_releasedate',
'type' => 'text_date',
),
),
),
return $meta_boxes;
}
Hope this helps!