There are several different reasons why you may be redirect to a login page when trying to access a HitSend link
If you have been given a HitSend Playlist Link and it takes you the HitSend Login page that means your original link was deactivated by the project owner. Project owners can deactivate and refresh links if they feel it is necessary for security reasons.
If you have received an invite to join a project you must create an account or log in with your current HitSend account. If you are not able to join with a HitSend account due to the invite link having been used already, this means someone else joined the project with this link as invite links can only be used by one person, and you should contact the project owner to receive a separate invitation.
In either situation, contact the project owner as they control link access to their projects.