You need to enable "Publish to web" for your account, you need to be Admin to do this, but it's disabled by default.
To enable it, in Power BI Service, go to "Settings", "Admin Portal", then "tenant settings", once there look for "Publish to web" under "Exporting and Sharing Settings". Enable the Settings you want, an click Apply. It'll take around 15 minutes to apply the setting, but then you should be good to go.
Hope this helps