I somehow missed this, but last Dec Apple started allowing app developers to opt in to allow sharing of in-app purchases with your family.
I only noticed when fiddling around with my app, but it may be worth checking if your favourite IAP can be shared.
The information in the app store isn’t the most helpful, but this is what to look for as far as I can tell.
I’ve been wondering about this but cannot confirm as I don’t have family sharing set.
Is it possible that even though the App Store page states that “Some in-app purchases […] may be shareable […] when Family Sharing is enabled”, it only work for some IAP items?
Both Airmail and Headspace state that they support Family Sharing, but the “Share with Family” switcher only exists in Airmail. Family Plan of Headspace looks like uses different method like Spotify does. Carrot Weather also don’t have the switcher, but it has a “CARROT Family Plan”.
The developer gets to choose which IAPs are shared and which are not.
My guess is that enabling this with just one IAP changes the message in the App Store to that rather vague one.