Does family sharing apply to in-app purchases?

Yes, it does. Make sure that purchases are shared in your family as detailed here:
https://support.apple.com/en-us/108774

This help article relates to the iPhone app called "Contacts Sync" which can be downloaded here: https://apps.apple.com/us/app/contacts-sync-google-more/id454390333
Need help?  You can email us at donald@playaapps.com