I am working on a commercial mobile app with some opening in the retail market but not a typical consumer app. Users would need to sign up to start exploring what the app can do. This app helps users to maintain their driving logs by pairing to an external device via BT and this device is plugged into their vehicle and collects driving data and sends back to the app.
In order to keep their app connected to this device, users need to buy a subscription plan. If they don't buy a subscription plan they can still use the app, the external device that collects data, still sends it to the app but the app restricts it from showing it to the user based on their subscription plan.
Is it ok to introduce subscriptions while users are signing up or should we let user's sign up and then introduce subscription plans? I'm redesigning the app and one thing to be noted here is when the user bought this external device, it has "Requires monthly subscription" text on the box. Also, the cost of this device is on the more expensive side, so anyone who bought the device for this cost would have done some research before buying it. So it's not that user is surprised with the introduction of subscription plans. However, assuming they would have done their research and should know about it is not something that sounds user-friendly.
Not sure if the background and question are elaborate enough to give the context of the problem. But any feedback or links on when is the right time to introduce subscriptions to the user would be helpful!