Chartarium is delivered for free in its basic version.
However, within the free version, some capabilities are locked or limited.
Substantially, it means that the stamps produced by Chartarium free, are not able to be customisable with the name of Your Organisation and that each page of the pdfs produced by the app will be watermarked.
In order to unlock Chartarium, press the Showcase menu button, sited on the top right of the main page. It will trigger the page pictured above, according with Your preferred Operating System (iOS, Mac OS or Android).
Ensure to be connected with Your preferred Store and to be able to make any purchase.
Chartarium provides a unique InApp Purchase named "Full Unlock". It means that once You'll unlock Chartarium, You'll be able to use Chartarium forever, with no more purchase or subscriptions. 
Press the BUY button and follow the OS instructions.
When all will be done, Chartarium will show a successful alert which will tell You that Your purchase is done and Chartarium is unlocked.
If You intend to unlock Chartarium out of the App, i.e. through Your preferred Store (Apple AppStore or Google Store), after done, open Chartarium and open the Showcase page, through the Showcase menu button of the main page, as explained above.
Your Store will tell to Chartarium that the purchase is done and Chartarium will confirm You that all is well done and the App is Unlocked.
If You have any question, please contact our tech support at chartarium@envisys.it
Thanks for Your purchase, thanks for encourage us to improve.