WooCommerce - Stamps.com API v1.3.2

Create shipping labels for USPS the smart way. With the Stamps.com integration, you can automatically create ready-to-print shipping labels for USPS, based on items in an order. Stamps.com seamlessly accesses the latest USPS rates when creating your labels, giving you unprecedented reliability, ease, and speed. This extension does not display shipping rates to your customers during the checkout process. If you want USPS rates shown on the cart/checkout pages of your site, you need to purchase the USPS Shipping Methods extension as well. Using these two extensions together, your customers see the best rates during checkout and you take advantage of those same rates when creating shipping labels via the backend order admin.

DEMO:
https://woocommerce.com/products/woocommerce-shipping-stamps/