Help Center login issue on Mac

One of our new customers has issues signing in on their Mac. They did mention that their browser does warn them about some disabled cookies but even after enabling the cookies they still can't sign-in to the system. Please see below for their message to us.

Replied and set up but cannot continue. At the page to enter the password, and after entering the password, have the following alarm.
Cookie is disabled in your browser. Please enable the cookie to continue.
On my mac in the privacy settings have disable and enabled and still have the same problem.
Can you help?