Hello Mpgarrote,
We see you might've already checked out this resource: If Shared Albums aren't working - Apple Support. We want to make sure you've followed the guidance in this section first to get started:
"What do I need to see and share videos, contribute to someone else's Shared Album, and add comments or like photos and videos?
- iPhone, iPad, or iPod touch with iOS 7 or later
- Mac with OS X Mavericks 10.9 or later
- Apple TV (2nd, 3rd, or 4th generation) with Apple TV software 6.0 or later
- PC with Windows 7 or later and iCloud for Windows
If the owner of a Shared Album turns on the Public Website option and shares the link with you, you can use any up-to-date browser to see photos and videos added by the owner and all contributors."
This article may also help to make sure everything is set up properly: How to use Shared Albums in Photos on your iPhone, iPad, and Mac - Apple Support.
Let us know if we can help with anything else at all or if this doesn't settle your issue so we can look into this further with you. Thanks and have a fabulous day!