Doesn’t update the app to full version during 50% off sale – SnoreLab : Record Your Snoring Review

I tried to buy the flash sale full upgrade version option which is for 3.99$. But when I tap the “NOW $3.99” button nothing happens and it doesn’t purchase the upgrade to the full version. Can you please help me to upgrade the app to full version?
Review by pavan16 on SnoreLab : Record Your Snoring.