Hey There! 

You can get the original_application_version field in the subscriber object from the response of the endpoint. This is only available on iOS and this will be null until an iOS receipt is sent for the user. After a receipt has been sent, it will indicate the first App Store version of your app that user installed.

Unfortunately, there isn't a way to retrieve this from our webhooks. 

More information on the fields that can be returned from webhooks can be found here: https://www.revenuecat.com/docs/event-types-and-fields#common-fields

disappointed!