Great to see you subscribed. We have the money back policy because we believe in our extension, and definitely, our support. It's just the right thing to do, and while we do give refunds when asked, it's a very rare event.
Anyways... regarding your issue with the Invite module, yup, that's a common problem. The Invite module uses an iFrame to Facebook (this is enforced by FB so that 'you' the admin don't have control over who people invite to your site). Unfortunately, the iFrame has had a multi-year bug that it tries to 'grow' itself when you hit invite, but the iFrame remains the same size. Facebook has never implemented a nice way around it, after countless requests from many developers.
In the module parameters, however, we have a workaround. It's not perfect, but works for most cases. Look for the "Enable Automatic Resizing" option and enable that. It uses some Javascript to detect when the content inside the iFrame increases in size and resizes the iFrame dimensions appropriately. Hopefully that will get you cleared up, but if not, let us know the page and we can help you get it working as expected.
Thanks again!