I want to implement Google Play In-app Billing v3 on an Android app so that the user can buy an item to remove ads. After the user buy this item, ads must not be displayed on any device logged into his/her Google account. As this app does not provide user accounts, I don't have a unique user identifier.

Do I need to store and validate purchases on my server or can I just rely on the Google Play In-app Billing library?