Magento 2 – Observer event is not triggering while using REST product API add

Below code is used to add product using a REST API. What I want to achieve is after adding product through the webservice I need to call an observer to perform data insertion to another table.

In the website through admin if I saved the product I am able call the observer but in the REST API it is not triggering.

// Post Data of Products
$sku = uniqid();
$productData = array(
    'sku'               => $sku,
    'name'              => 'Simple Product ' . uniqid(),
    'visibility'        => 4, /*'catalog',*/
    'type_id'           => 'simple',
    'price'             => 0.00,
    'status'            => 1,
    'attribute_set_id'  => 9,
    'weight'            => 1,
    "extension_attributes"=> [
        "stock_item"=> [
            "manage_stock"=> 0,
            "is_in_stock"=> 1,
            "qty"=> "0"
        ]],
    'custom_attributes' => array(
        array( 'attribute_code' => 'category_ids', 'value' => ["3"] ),
        array( 'attribute_code' => 'description', 'value' => 'Simple Description' ),
        array( 'attribute_code' => 'short_description', 'value' => 'Simple  Short Description' ),
        array( 'attribute_code' => 'chef_name', 'value' => 'Rafsan Chef' ),
        array( 'attribute_code' => 'servings', 'value' => '2 people' ),
        array( 'attribute_code' => 'cooking_time', 'value' => '20 minutes' ),
        array( 'attribute_code' => 'pdf_upload', 'value' => '123.pdf' ),
        array( 'attribute_code' => 'steps', 'value' => 'step 1 content###Step 2 content###Step3 Content' ),
        )
);

// creating Product using Magento 2 Rest API
$productData = json_encode(array('product' => $productData));
$ch = curl_init("http://127.0.0.1/magento/index.php/rest/V1/products");
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch,CURLOPT_POSTFIELDS, $productData);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/json", "Authorization: Bearer " . json_decode($token)));

$result = curl_exec($ch);

// the Product is Created using the Above Code 

// i have created an observer in magento for product save after, that observer is working if it is saved from website admin End. but not working while saving through Rest Api. 

// events.xml file created in app/code/[NAMESPACE]/MODULE_NAME/etc/adminhtml/events.xml

<event name="catalog_product_save_after">
        <observer name="cus_recipe_saveafter" instance="FreshboxRecipesObserverProductsaveafter" />
</event>