How to assign specific attribute to variation for woocommerce product?

I am creating a product with variations:

// Creates a product

        $post = array(
         'post_title'   => $title,
         'post_content' => $description,
         'post_status'  => "publish",
         'post_excerpt' => $excerpt,
         'post_name'    => $slug, //name/slug
         'post_type'    => "product"
 );


$new_post_id = wp_insert_post( $post);

// Creates needed attributes

$product_attributes = array();

$product_attributes['print_size'] = array(
    'name' => 'print_size',
    'value' => implode('|', $availableSizes),
    'position' => 0,
    'is_visible' => 0,
    'is_variation' => 1,
    'is_taxonomy' => 0
);

$product_attributes['paper_type'] = array(
    'name' => 'paper_type',
    'value' => implode('|', $availableMaterial),
    'position' => 0,
    'is_visible' => 0,
    'is_variation' => 1,
    'is_taxonomy' => 0
);


update_post_meta($new_post_id, '_product_attributes', $product_attributes);

// Creates variation

$my_post1 = array(
    'post_title' => 'SizeType122',
    'post_name' => 'post_name222',
    'post_status' => 'publish',
    'post_parent' => $new_post_id,
    'post_type' => 'product_variation',
    'guid' => home_url() . '/?product_variation=1' 
);

$attID1 = wp_insert_post($my_post1);

update_post_meta($attID1, '_virtual', 'no');
update_post_meta($attID1, '_downloadable', 'no');
update_post_meta($attID1, '_manage_stock', 'no');
update_post_meta($attID1, '_stock_status', 'instock');
update_post_meta($attID1, '_sku', '300');
update_post_meta($attID1, '_price', '300');

It creates a variation with attributes as it should, but if I check product variation it brings me something like this:

Array
(
    [0] => Array
        (
            [variation_id] => 1542
            [variation_is_visible] => 1
            [variation_is_active] => 1
            [is_purchasable] => 1
            [display_price] => 300
            [display_regular_price] => 300
            [attributes] => Array
                (
                    [attribute_print_size] => 
                    [attribute_paper_type] => 
                )
  [image_src] => 
        [image_link] => 
        [image_title] => 
        [image_alt] => 
        [image_caption] => 
        [image_srcset] => 
        [image_sizes] => 
        [price_html] => 
        [availability_html] => 
        [sku] => 300
        [weight] =>  kg
        [dimensions] => 
        [min_qty] => 1
        [max_qty] => 
        [backorders_allowed] => 
        [is_in_stock] => 1
        [is_downloadable] => 
        [is_virtual] => 
        [is_sold_individually] => no
        [variation_description] => 
    )

)

So attribute is empty and if I go to admin side I can see “any print size” and “any paper type” as variations. If I select specific attributes and save in the admin I can see these values in the array which I shared up top filled :

  [attributes] => Array
                (
                    [attribute_print_size] => 8x10
                    [attribute_paper_type] => Enhanced Matte Paper
                )

So how I could do this programmatically?

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