On your Mac, choose Apple menu > System Preferences. On your iPhone, iPad, or iPod touch, go to Settings > iCloud > Photos and open iCloud Photo Sharing.
To share photos and videos to other person via iCloud Photo Sharing on your computer or iPhone, you should ensure that this iCloud feature is enabled on these devices. Enable iCloud Photo Sharing on iPhone/Windows/Mac/Apple TV An iCloud Alternative to Transfer Photos from iPhone to PC
Re-invite Your Friends to the Shared Album
Enable iCloud Photo Sharing on iPhone/Windows/Mac