The pre-paywall stage is what the user experiences after installing your app. This means that (s)he was already engaged enough to tap “Get” and wait while the app was installed and (s)he is ready to discover your app where (s)he will have to learn the experience you designed before deciding to pay for your app or not.
It is in this stage where the user tries to understand the details of the features that (s)he thought was included in the app. This is why it is important to explain your features in detail so that the user is reassured that his/her need will be satisfied. This s also an opportunity to showcase the user experience of the app: if you can show that it is easy to use with a simple interface, the user will be more inclined to try out the app. And last but not the least your paywall must be clear and visible, or simply put accessible: we still see too many paywalls that are hidden in some way which prevents users from signing up.