In general - you will be charged 3 Eur monthly fee (paid for the full year in advance, as a 36 Eur annual fee). You will receive two notifications before the end of the free GSM service period (which is 2 months). When GSM service expires - you will be able to renew your account from Monimoto app.
Currently, the payment functionality is not yet implemented in our app, so you can continue for free. Once it is ready - we will inform all users by push notifications, most likely in 2018 Q2.