Meeting Invitee Access

A few of my meeting invitees are unable to join my meeting using the Invite link or have difficulty, i.e. are asked for passwords or authentication codes.    One sent me a screenshot of the error message she received:  blob:https://mail.proton.me/ec516750-6fe3-4830-af30-b638ee5f0d61  Please help,  I am beyond frustrated.