Hi, all devices must be iOS 14.6 or higher. Here is a list of common solutions to sharing issues,
Here is an Apple Support article that goes over adding Participants and Co-owners,
https://support.apple.com/en-us/HT212020
Here is a list of items that may quickly resolve your issue,
- all iPhones must be iOS 14.6 or higher
- turn off VPN
- log out and in to your Apple ID
- ask Participants and/or Co-owner to log out and into their Apple ID
- make sure you and participants are currently in US.
- make sure Participants and Co-owner has Apple Cash setup in Wallet App
- Family Group members should update their age in Apple ID. >> https://support.apple.com/en-us/HT204164
- Participant must be using same Apple ID they use for Family Sharing Group
There recently has been some evidence that the issue might be related to using vintage Apple ID that uses .Mac and possibly .Me.
In my case it was related to my wife not having Apple Cash setup before I invited her. I had to delete the invite, setup Apple Cash and then re-invite her.
I hope this helps.