Apply a coupon to WooCommerce order using rest api

Question

In woocommerce, we can add a discount to any order using the Coupons feature (fixed amount, percent amount…).

I tried this code:

function ocost_check_coupon(WP_REST_Request $request){
    $coupon_code = $request->get_param('coupon');
    $order_id = $request->get_param('order_id');
    global $woocommerce;
    $coupon = new WC_Coupon($coupon_code);
    
    // Get the coupon discount amount (My coupon is a fixed value off)
    $discount_total = $coupon->get_amount();
    
    // Loop through products and apply the coupon discount
    $order = wc_get_order($order_id);
    foreach($order->get_items() as $order_item){
        $product_id = $order_item->get_product_id();
    
        if($this->coupon_applies_to_product($coupon, $product_id)){
            $total = $order_item->get_total();
            $order_item->set_subtotal($total);
            $order_item->set_total($total - $discount_total);
            $order_item->save();
        }
    }
    if ($order->save()) {
        $results = array();
        $results = array(
        'status' => 'true',
        'message' => 'done and apply coupon to order',
        );  
        return $results; 
    } else{
        return array(
            'status' => 'error',
            'message' => 'error to complete coupon function'
            );
    }
}

But it doesn't seem to apply any coupon. I just added code into the order: how can check before apply coupon if this coupon found in wp-admin or not?

Any help will be appreciated.