What ux method can I use to verify the success of Subscription Model of my app?

I'm currently have an application project but I cannot disclose more information about it. I would like to know what specific methods can I use to verify if the "Subscription Model" idea that I have is going to work properly. Meaning, I can assure that the users will not unsubscribe and keep on paying on the application. The application does have already a wide network of possible customers so I the first launch will be critical.

Thanks!