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ShippingEasy integrates with the backend of your WooCommerce store to assist with the management and shipment of your orders. Unfortunately, the plugin is not designed to integrate with your shopping cart so I certainly understand why you are looking at plugins that may help you set up live shipping rates on your WooCommerce site. When looking at WooThemes, I found this one: USPS Shipping Method
Since your Endicia accounts can only be used in ShippingEasy and the plugin is asking for USPS credentials, I would recommend setting up an USPS account directly on the USPS site. https://reg.usps.com/register
Or if you can bypass the USPS credentials and just use our rates, you are welcome to view our rate tables in order to set that up: ShippingEasy's USPS Rate Tables