I had the same problem, needing to activate a second sim (for an internet router). Didn't manage to use the same email address but used instead a second email address. I think the problem was that my dashboard kept logging in automatically to my first sim account (so no activation options). Logging off that enabled an activation for the second sim to be made via smarty.co.uk/activate, using the second email and a second account. Then I invited the second sim to the Group of the first sim (all rather fiddly). Fortunately the second account could be verified with an option to get the 6 digit code by email instead of to the mobile number of the second sim (which is in the router). Phew (took about 2 hours searching help and trying different things) !