Someone cannot open what I shared

The person you sent it to sees, instead of your artifact:

This artifact is private. Sign in with an account that has access.

Or, after signing in, their address followed by:

does not have access to this artifact

Or, opening a share link:

Whoever shared it has stopped sharing it this way, so it no longer shows here. If you still need it, ask them for a new link.

Or, opening an artifact that is offline:

It is not gone: once a version of it is live again, it is served here.

New artifacts start private. Someone can open one only if a row of its access list lets them in — their address, everyone at their domain, a share link, everyone in the workspace, a sign-in provider, or anyone with the address — and they are signed in, or have proved their address, as that row asks. A share link that was revoked stops letting anyone in at once. An artifact with no live version — taken offline, or with every version staged — serves nothing.

Open the artifact's Share list and check who it lets in: add the person's address, or everyone at their domain, or make a share link and send them that (Control who can see it, Share a private artifact). Ask them to sign in with the address you added. If it is offline, make a version live again from the artifact's Versions card.

Still stuck? Write to support with the artifact's address.