I'm having the same problem too
I've had the same issue; just takes me back to the log in page every time. Doesn't come up with the option to "Start Free Trial" that the Samsung website suggests
I haven't managed to get the calm offer to work but I did find a workaround for Disney+.
Allowing all cookies in the browser seemed to do the trick. So, if you're using Chrome press the three dots in the top right, go to settings>site settings>cookies>allow all cookies.
This worked for me, although not for calm.