I have tried with a couple of tests with public repo I have under my GitHub account(A) using another account (B) as collaborator
I go to
Settings > Manage Access > Invite collaborator : Insert my account (B) id
Then I got the invitation mail for my account (B) with the "view invitation" button having a link like:
github.com/[accountA]/[repository-name]/invitations
But I got a 404 page, as if, account B doesn't have privileges to view it.
And under accountA -> settings->manage access I have the collaborator B still pending invitation, but an update under DIRECT ACCESS box saying : "1 has access to this repository. 1 invitation."
My first try was with a private repo, but then I tried also with a public repo and got same unexpected behaviour.
How can I solve this? Am I missing something?