You need to enable the xml dump for the request/response on the checkout page (Configuration - Settings - RTShipping.DumpDebugXmlOnCheckout - true - Refresh Store), then while logged in as an Admin for the site, take a valid product to the checkout (make sure it is a single item or no more than .81 pounds worth of stuff), and enter a valid international address. That should provide your shipping methods, and scrolling down should reveal the request and response. Make sure your package weight is sent below the 0.82 limitation (must be 13 ounces or less total weight).
If it isn't, check the following settings:
MinOrderWeight (must be below 0.82)
RTShipping.DefaultItemWeight (must be below 0.82 when a product has no explicit weight entered)
RTShipping.PackageExtraWeight (should be 0 or low enough not to blow the total weight of 0.81)
RTShipping.ShippingMethodsToPrevent (should not contain the International First Class method)