Stretch database feature is default disabled. To use it , it must be enabled. In case you try to use it without enabling it , GUI will show a message you to enable the feature

Pre-Check

Change the configuration value of [remote data archive]   to 1

use master
go 
sp_configure 'remote data archive',1
reconfigure with override 
go

Once the configuration value is overridden , the GUI will provide you the option to login to Microsoft Azure

On Successful login.You will see all you subscription as below