Unable to activate full features – Santoor PRO Review

First i installed free version and i was intrigued to buy pro version and there was also a button for upgrade which at the moment i did not cared about. Well i paid 9.99$ and surprisingly within app i still get same message. In setting there is claim subscription but after clicking it message 'purchase request can not continue (null)' shows up. Upgrade option is still exists in pro version and asks you for 0.99$ which i still don't understand it's reason. I paid for this only because i love Santoor and among what i found on AppStore it is best. But it need serious support which i kindly ask developer to provide.
Review by b2never on Santoor PRO.