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You can use the Microsoft Store collection API and Microsoft Store purchase API to access entitlement information for these products from your services. These APIs consist of REST methods that are designed to be used by developers with add-on catalogs that are supported by cross-platform services. For example, Microsoft Store collection API could query for products owned by a user and Microsoft Store purchase API could get subscriptions for a user.
You could learn the full process about how to use the Microsoft Store collection API and Microsoft Store purchase API here: Manage product entitlements from a service. And if you want to get the subscription information of the user, you could take a look at Get subscriptions for a user, which contains the full request example and response body.
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