Definition of 

Crossgrade
What's 
Crossgrade
 : it is one of the possible values for 
Event
. It means:
Subscriber switched between standard price subscriptions of the same level in the same subscription group. If the subscriptions are of the same duration, the crossgrade is counted when it goes into effect immediately. If the subscriptions are of different durations, the crossgrade is counted when it goes into effect on the subscriber’s next renewal date, as opposed to when the subscriber switches their subscription, which could be in the middle of the period.
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Trends: Subscriptions Events
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App Store Connect