Start with the right checks.
A valid link does not necessarily grant access. The account, library and sharing permissions all need to match the intended recipient.
What to do next.
Read the full error and confirm which account is signed in.
Compare the invitation with the address you are using.
Ask the file or site owner to confirm the required access and the intended link.
If no access request option appears, give the administrator the site address and error rather than changing site settings yourself.
Check the result.
Open the document with your own authorized account and confirm the expected view or edit permission.
Stop and get help if…
Ownership is unclear, external sharing is restricted or the issue affects a whole team. Access changes need approval from the responsible owner.

