The FastSpring plugin does not have enough resources behind it. It keeps breaking and 6 months later with no solutions or follow-ups, I just gave up and put a link to the onfastspring.domain.com page and moved on. I would have dumped FS over this and so many other techSupport nightmares for 2+ years, but WooCommerce can’t distribute predetermined serial numbers like FS. Outside of that WC works so much better and has more options for a WP store – like catalogs, and searches, etc…
