According to the documentation in the below link, Apple subscriptions status server will send this field expiration_intent when users renew their subscription.
Apple's
This is the same as the Subscription Expiration Intent in the receipt. Posted only if notification_type is RENEWAL or INTERACTIVE_RENEWAL.
I'm getting all the notifications on my production server and have checked all the logs for RENEWAL or INTERACTIVE_RENEWAL types but never been able to get the value for this field.
Any idea why this is happening? though I'm getting the rest of the fields with their values.