creating product with variations using woocommerce REST API

you have to create another request for variation.

$variation_data = [
    'regular_price' => '15.00',
    'image'         => [
        'src' => 'https://shop.local/path/to/image_size_l.jpg',
    ],
    'attributes'    => [
        [
            'id'     => 5,
            'option' => 'L',
        ],
    ],
];

$this->woocommerce->post( "products/$product->id/variations", $variation_data );