How to retreive subfield value

Hello Rilwis, thank you for this great extension, I am able to retrieve the parent values, but not the values from the subfields, here is my code:

add_filter( 'rwmb_meta_boxes', 'saq_metas' );
function saq_metas( $meta_boxes ) {
	$meta_boxes[] = array(
		'title'  => __( 'Questions and Answers' ),
		'post_types' => 'saq',
		'fields' => array(
			array(
				'id'     => 'saq_id',
				'type'   => 'group',
				'clone'  => true,
				'sort_clone' => true,
				// Sub-fields
				'fields' => array(
					array(
						'name' => __( 'Question', 'bs_saq' ),
						'id'   => 'question',
						'type' => 'text',
					),
					array(
						'name'    => __( 'Answer', 'bs_saq' ),
						'id'      => "answer",
						'type'    => 'wysiwyg',
						'raw'     => false,
						'std'     => esc_html__( '', 'bs_saq' ),
						'options' => array(
							'textarea_rows' => 4,
							'teeny'         => true,
							'media_buttons' => false,
						),
					),
					array(
						'name'   => __( 'Supplementary Information', 'textdomain' ),
						'id'     => 'supplementary',
						'type'   => 'group',
						'clone'  => true,
						'fields' => array(
							// Sub title
							array(
								'name'  => __( 'Supplementary info title', 'textdomain' ),
								'id'    => 'sub_text',
								'type'  => 'text',
							),
							// Sub info
							array(
								'name'  => __( 'Supplementary info text', 'textdomain' ),
								'id'    => 'sub_textarea',
								'type'  => 'textarea',
							),
						),
					),
				),
			),
		),
	);
	return $meta_boxes;
}

I would really appreciate if you can guide me, I tried this:

$group_values = rwmb_meta( 'supplementary' );

    foreach ( $group_values as $group_value ) {
        $value = isset( $group_value['sub_text'] ) ? $group_value['sub_text'] : '';
        echo $value;
    }

but it says to me "Warning: Invalid argument supplied for foreach() in" on line 19 and line 19 is this one:
foreach ( $group_values as $group_value ) {

I am confused, please help, thank you!