Paid apps are the most straightforward approach. At the moment of uploading the application to Google Play, we set the download price. As mentioned just now, some applications have a freemium version that includes advertisements or, for example, have limited functionality. And then, we have a paid version that can be considered the full, professional version or the one without advertisements.
When we created an application in Google Play, under the pricing and distribution section, we can choose whether we would like to publish it as free or paid. A paid application can always be converted to free, but a free application, once it has been published as free, cannot be changed to paid:
The only option would be to change the package name and upload it as a brand new application. For more information, refer to https://support.google.com/googleplay/android-developer/answer/6334373?rd=1#paid_free.
We have to set the price of our application. There is a default price...