Hi,
Ok, I gave the system a refresh, you can now download it again from the wiki:
https://hutonggames.fogbugz.com/default.asp?W1003 and it support the current asset store version of Parse, v1.3.0
The demo should now work, and you should not have any warnings.
As for what you can do once you are logged in:
yes, indeed you can use Parse to record IAP purchases and receipts, it's totally up to you to define how you want to integrate such system tho, since Parse is a totally flexible solution, you can create any object with any properties. It's indeed very powerful!
Also, IAP is indeed a very complex feature, and Parse is not the answer on its own, a very deep and careful analys and study of what IAP is mandatory before touching on the subject.
however, you will find a lot of assets on the asset store that will make the process easier like this for example
http://www.rebound-games.com/?page_id=48I would definitly encourage you to study existing solutino offering a support for IAP before trying to deal with it up front yourself.
Bye,
Jean