Hi Suzanne,
You'll need to give the user attempting to access the mobile version of Method permission to do so before they will be able to log in this way. You can do this by navigating to the Customize tab and clicking on the Users tab link. Here, youll want to scroll down to the Edit an existing Users section and clicking on Edit... beside the user you are trying to give mobile access to.
On Step 1 of the Edit User process, you will see a checkbox with the text Enable mobile Login beside it; check this box and press Finish. When this User next logs in, they should see the option to sign in to the Mobile version of Method.
Thanks Suzanne!
Regards,
Ben