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Does MS store take care of upgrade or I have to program for upgrade?
You need to write some code in your app to mandatory package updates. The mandatory status of a package update is not enforced by Microsoft, and the OS does not provide a UI to indicate to users that a mandatory app update must be installed. Developers are intended to use the mandatory setting to enforce mandatory app updates in their own code.
You could refer to this document for more information about the code sample: Mandatory package updates.
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