When you add the Teams Service to the account, you will have the option to Sync your users.
This means that you will be able to synchronise with Office365 making it easy to build the list of users to be added to the account.
With this option disabled, you will need to manually enter each user.
Following a successful sync you will not 'automatically' see your users appear on the Users page.
However, a full list of users has been built in the background and these will be available from the drop down when adding users. No such drop down appears if users are to be entered manually.
Once users have been added it is a good idea to re-sync with Office365 to ensure any manual changes are pushed up to Office365.
None of your users have phone numbers assigned in Office365
If after running a Sync you see the message "None of your users have phone numbers assigned in Office365" then it means that you have not set a phone number on any of your users in Office 365.
To resolve this you should use the Office365 Skype for Business legacy portal to assign phone numbers to your users.
Users do not appear in the Add Users list.
If, following a successful sync (green ticks) you cannot see any users in the Add User drop-down, this might be caused by existing plans/services in Office365. Please remove any/all non-required calling plans that may previously have been used.
A debug Sync can also be performed on the portal which provides greater diagnostics we can use in assisting you in this regard. A debug-sync is performed by holding Alt-Shift when clicking the Sync Now button.