Hi there! You can purchase the insurance 2 different ways--you can set up your Auctiva account so that when a buyer wants insurance on their package it will automatically be purchased through Auctiva Shipping Insurance and there's nothing else you need to do. If you do not want to have the insurance policies automatically purchased whenever a buyer wants it, you can log onto your Auctiva account and purchase the policy manually on your Sales transactions page.
Just remember that if insurance is desired for a package and you print out the labels using PayPal/ebay, do not purchase the USPS insurance--the policy will be automatically generated if you have set up your Auctiva account to do so. And if you do not have your account set up to automatically purchase the insurance, you still have a couple of days to buy it on Auctiva (the post office won't let you do that!)
Hope that helps a bit...I've been using the insurance for 6 months and I haven't had any problems using it so far...good luck!