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I‘ve got a response from the store team to your question. Based on the red note here - Set add-on pricing and availability, it mentioned that "Choosing the Stop acquisition option and/or submitting an app update that removes the add-on from your app will not prevent customers from using the add-on if they have already purchased it. Existing subscriptions will fail to renew and subsequently be canceled after the current term ends.". If you removed the subscription add-on, the customer will not be able to renew it and it will expire after the current term ends.
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