Just to clarify, there are 2 paths to upgrading to Infuse Pro for free.
When Infuse 2 was announced in October (http://blog.firecore.com/11009), we added the Infuse Pro In-App purchase at set the price to free until Infuse 2 was made available. From what we saw, most users used this path to ‘purchase’ Infuse Pro for free. This method is no longer available (well it is, but it’s not free) since Infuse Pro now costs $4.99
As a fallback, in Infuse 2 we’re using receipts to detect which version of Infuse was oriignall purchased. If 1.5 or earlier was your first version, simply tapping the Restore button on the purchase prompt should skip over the In-App purchase step and just unlock the Pro features for you.
Hope this helps.