If the app has not been updated after you've made your purchase of Opera VPN Gold don't worry!
You are able to restore your purchases from the Opera VPN app, which will update Opera VPN to Opera VPN Gold.
Please ensure that you are logged in with your Apple ID, in the App Store in which you made your purchase, then follow the instructions below:
Step 1: Tap on the menu
You should now be able to select your Opera VPN Gold subscription. Once it has been selected the Opera VPN application will update to Opera VPN Gold.