Google Play : An error occurred while getting the status of your purchase
Silly me, I was trying to purchase the app with the same Google account as the one I use for publishing apps, which is clearly forbidden by Google's policies : 


  Please note that it is against Google’s policies to purchase your own
  application. You will receive an error message when you try to
  purchase your own application.


Pitty that the error message wasn't a bit more helpful, but the mistake was mine anyway.