Google Analytics & Gumroad Integration

We run a Gumroad shop and have it linked to Google Analytics. Unfortunately, it doesn't seem to be setup correctly. It is not tracking all of the sales that we are making, and GA is coming back with data that doesn't match our Gumroad dashboard.

I need some one to fix this and show me how to view the data correctly inside of GA so we can start using our data properly.

In exact terms, this is what I need.

> Get the data from our Gumroad shop www.futurephonic.co.uk (which currently redirects from a 123reg account to our Gumroad shop www.gumroad.com/futurephonic) to show up in our GA account as accurately as possible.

> Explain to me why it currently isn't very accurate - for example last this week we sold 22 of a product and GA is only showing 8 sales.

> Show me how GA is getting its "Revenue" field as this seems completely unrelated to any actual amount of revenue we are generating. Fix this so that it accurately represents our revenue.

> Explain / demonstrate how the problem will be fixed

> Fix the problem and show me your working.