clone _as_multiple not working

Hi there, tried a few times to save clone as multiple, but does not work, data on database still the same serialized string.. code :

 [
                'id'                => $prefix . 'rdo_staff_group_D',
                'type'              => 'group',
                'fields'            => [
                    [
                        'id'         => $prefix . 'rdo_staff_D',
                        'name'       => esc_html__( 'Funcao', 'text-domain' ),
                        'type'       => 'select_advanced',
                        'options'    => [
                            'armador'  => esc_html__( 'Armador', 'text-domain' ),
                            'soldador' => esc_html__( 'Soldador', 'text-domain' ),
                        ],
                        'js_options' => [
                            'size' => 25,
                        ],
                        'columns'    => 3,
                        'add_button' => esc_html__( '+ funcoes', 'text-domain' ),
                        'size'       => 25,
                    ],
                    [
                        'id'      => $prefix . 'rdo_staff_DH',
                        'type'    => 'number',
                        'name'    => esc_html__( 'HHT', 'text-domain' ),
                        'min'     => 1,
                        'max'     => 9,
                        'step'    => 1,
                        'columns' => 5,
                        'visible' => [
                            'when'     => [['rdo_staff_D', '!=', '']],
                            'relation' => 'and',
                        ],
                    ],
                ],
                'clone'             => 1,
                'default_state'     => 'collapsed',
                'collapsible'       => true,
                'group_title'       => '{rdo_staff_D}',
                'add_button'        => esc_html__( '+ adicionar MO', 'text-domain' ),
                'save_state'        => true,
                'tab'               => 'rdo_staff_tab',
                'clone_as_multiple' => true,
            ],

result : a:1:{i:0;a:2:{s:11:"rdo_staff_D";s:7:"armador";s:12:"rdo_staff_DH";s:1:"9";}}

Any help?

thanks