Same for me, I tried also accepting the terms and conditions at icloud.com like other's mentioned, still no luck. Even when I sign in in the simulator settings under sandbox account, I go through all the steps then once complete, it just shows "Sign In" again... Can't even test in-app purchases properly, a shame because its real user's money and testing in sandbox is not possible

Same, I also accepted the terms and conditions on icloud.com after signing in with the sandbox user. Very sad, waste of time