I think you're slightly mixing up two different types of this earning method.
When talking about SDK -- that's when you're the owner of an app, like some casual match-3 game. You then approach major proxy providers like Bright Data with their EarnApp and offer to integrate their SDK into your app, allowing them to farm proxies from your users. Here, payment terms will depend specifically on your situation -- your app type, audience, countries, and so on.
But if you just want to install an application on your own phone, that's not an SDK, that's just a regular app. For example, Honeygain. Here, too, the specifics depend on your geolocation, uptime, and traffic type.
Generally, you won't earn much this way as a person (not the app owner). Plus, some of these services have issues with reputation -- both in terms of payouts and risks related to how your traffic might be used. Is it worth it for these small amounts of money? That's a complicated question.
If you genuinely have access to phones and inexpensive mobile data, you can easily sell that as a proxy farmer. Various ways of doing this have been discussed extensively right here on this forum, in neighboring threads.