Three distinct issues might be happening:
1. The most common is that the files are not available because the invitation was not yet accepted.
This happens when the Referee did not yet accepted the invitation. As a result the files are not made available, like shown in the image below.
All that is required is for the Reviewer to accept the invitation. The page will reload and the original files will appear and be available for download.
2. The LINK itself does not open the system and instead shows a page not found error.
This happens when the e-mail client breaks the direct link in two lines making the link itself broken also, as shown below:
a. Log in the system using the login and password and going to the Reviewer Panel. This might require new users to use the “Forgot your password?” link in order to gain access.
b. Other solution is to reconstitute the original link by copying both parts and pasting them together on the browser.
3. Files not available even after Reviewer accepts the invitation.
In this case probably what happened is that the Administrator or Editor did not mark the files that should be available to the Reviewers before sending the invitations. The images below show both original and revised files not marked (checkbox):
The Administrator or Editor must access the paper details page and check the files that need to be made available to the reviewers.