All your devices are using the same Apple ID?
Make sure notifications haven't been disabled. This article discusses notifications --> Use notifications on your iPhone or iPad - Apple Support
Make sure the software is up to date on all devices involved.
If an app or feature on your device is not working, it may have been disabled using Screen Time, or by an IT administrator if you are using a device owned by an employer or educational institution. See how to use Screen Time on an iPhone, iPad, or iPod touch by clicking here --> Use Screen Time on your iPhone, iPad, or iPod touch - 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, iPod touch, Apple TV, or Mac - Apple Support
Sign in with your Apple ID - Apple Support
● 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