Make sure you've done as instructed in --> Add a family member to your shared subscriptions - Apple Support
Here's a list of standard things to try when a feature is not working:
Make sure the software is up to date on all devices involved.
Update macOS on Mac - Apple Support
Update your iPhone or iPad - Apple Support
Sometimes it helps to have the devices involved take a fresh look at settings:
● If this is a service, try disabling it and turning it back on.
● Try signing out of accounts and back in again.
Sign out of iCloud on your iPhone, iPad, Apple TV, or Mac - Apple Support
Sign in with your Apple ID - Apple Support
If you have more than one Apple ID, don't forget you may be signed into other accounts too for special services such as iMessage and Media & Purchases.
● Restarting is a simple step that can resolve many unexpected behaviors.
iPhone: Restart your iPhone - Apple Support then choose your model.
iPad: Restart your iPad - Apple Support
Mac: Ways to start up your Mac - Apple Support
Try using other equipment if possible. I have seen several cases where somebody tried to do something on one item of equipment and failed, but then tried on a different item of equipment and succeeded.
Sometimes it can take some time for changes to propagate through the system and waiting may help ( e.g., Family Sharing of Apple News+ - Apple Community ). If a problem persists, particularly over several days, try contacting Apple for assistance:
Click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
"See a list of Apple phone numbers around the world."
Click here --> Contact Apple for support and service - Apple Support