tell me if I pay for 1 month and place the app in the store, and the next I forget to pay for what will happen.?
You can stop your pro plan at any time and your app will continue to be available in the app stores. However, you will just no longer be able to create new builds to update that app until you are back on the paid plan.
will my user base remain ?
Yes, it will still be there.
The question is not on the topic. But I don’t know who to ask anymore. Is it possible to connect another payment system ?