Design the mobile and backend API flow for controlling access limits to different AI model versions in a ChatGPT-like mobile app.
Requirements:
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The product offers multiple model versions, and each model may have a different free usage quota.
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The mobile app must know whether the current user can access a selected model.
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If the user exceeds the free quota, the app should show a toast explaining how long remains until the next free access becomes available.
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The toast should also provide a link or call-to-action that lets the user upgrade to a paid plan.
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Provide backend endpoint designs.
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Provide a mobile-side architecture using MVI or MVVM.
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Provide representative function signatures for the mobile client and backend contract.
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Assume the mobile implementation is Android-focused, but the API should be platform-independent.