Definition of 

Upgrade from Introductory Offer

What's 
Upgrade from Introductory Offer
: it is one of the possible values for
Event
. It means:
When a customer switches from a subscription in a lower level to a subscription in a higher level. The introductory offer ends immediately and the customer’s prorated amount from the prior in-app purchase is refunded to the original payment method. The new in-app purchase is charged and goes into effect immediately at the full price, which changes the customer’s renewal date to the upgrade date.

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Trends: Subscriptions Events

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App Store Connect

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