Hello MGS8809,
Thanks for posting in the Apple Support Communities.
Can you explain where and what the family member was doing when this error was received? For example, were they connected via cellular or Wi-Fi? Were you sharing a third-party app, or were you trying to invite them to use your iCloud subscription, or similar? This can help us isolate to network connectivity, a particular app, feature that isn't working properly, etc.
It's also a good idea to double check that the family member is updated to the latest iOS release, so that an outdated iOS can be ruled out as the culprit.
- How to back up your iPhone, iPad, and iPod touch - Apple Support
- Update your iPhone or iPad - Apple Support
Best regards.