How to show loading gif like AJAX request from start of the InitiatePurchase to Complete?

Hi,

I am implementing Unity iAP to my game. I have non-consumable goods for sale, at the current version of Purchase script, Buy process starts with InitiatePurchase function and ends whever ProcessPurchase.Complete action is returned. Within this process, I would like to block all bacground elements and show a gif just like we do at Ajax requests. However, I can not find a proper way since the API is a bit closed.

Is there any ideas how to achieve this?