Subcription to apps

I have made an app which is presently free. I have not uploaded on play store yet. I want the app to be paid with subscription. Basically there is one button in the app which i am intent to keep it disable for free and enable to subscribe customers.The app is absolutely offline. I have seen certain videos and gone about the community but not understood much. What in broadly understood is that I need to create a product id after uploading the app(with button disable) on store. So I will first upload the app with button disable on play store, wait till the time it is accepted, then create a product id for the app and then recreate the app using in app billing in kodular with this product id and upload again as update. Please suggest me is this the procedure or I am doing mistake somewhere?
Thanks in anticipation

Understood for in app single purchase but what for subsiption and why do I need this extension. Is this is not possible by the in app component.

Read my answer here