When you use licenses from Microsoft in your VDC environment you are required to report on SPLA. All software apart from Windows Server OS needs to be reported.
Once you have reported a license it will automatically be reported every month. On the 25th of every calendar month a notice will be sent by e-mail to all Super Admin roles in your organisation with a reminder that it is time for the monthly reporting. You only need to report once you have made a change. If there is no change you will continue to be invoiced based on the previous month.